Zucchini Tomato Gratin

There’s a certain magic that happens in the kitchen when the seasons turn, especially at the tail end of summer. My garden, or more accurately, my overzealous haul from the local farmer’s market, often leaves me with a bounty of zucchini and tomatoes, their vibrant colors practically begging to be turned into something spectacular. For years, I struggled to find a dish that did them both justice, a dish that my entire family would devour without a single complaint about “too many vegetables.” Then, this Zucchini Tomato Gratin entered our lives, and everything changed. The first time I pulled this dish from the oven, the aroma of roasted garlic, sweet tomatoes, and savory herbs filled the house. The top was a perfect, crunchy blanket of golden-brown breadcrumbs and cheese, bubbling invitingly around the edges. My kids, usually skeptical of anything green, were drawn in by the cheesy allure. That night, the baking dish was scraped clean. It wasn’t just a side dish; it became the star of the meal. This gratin is more than just a recipe; it’s a celebration of simple, fresh ingredients transformed into pure comfort food. It’s the dish I bring to potlucks, the one I make on a cool evening, and the recipe that proves, once and for all, that vegetables can be the most decadent and satisfying thing on the plate.

Ingredients

• Zucchini: 2 lbs (about 4 medium). Look for firm zucchini with smooth, unblemished skin. This is the star vegetable, providing a tender, slightly sweet base.
• Tomatoes: 1.5 lbs (about 4-5 medium Roma or on-the-vine tomatoes). Ripe, flavorful tomatoes are crucial as they release their sweet juices and create a natural sauce.
• Kosher Salt: 1.5 teaspoons, divided. Used to draw excess water from the zucchini and to season the entire dish.
• Olive Oil: 3 tablespoons, extra virgin. A quality olive oil adds a fruity, peppery depth of flavor for sautéing and drizzling.
• Yellow Onion: 1 large, finely chopped. This builds the foundational aromatic layer of the gratin, adding a sweet and savory depth.
• Garlic: 4 cloves, minced. Fresh garlic is non-negotiable for that pungent, aromatic kick that permeates the entire dish.
• Dried Oregano: 1 teaspoon. Adds a classic, earthy Mediterranean flavor that pairs perfectly with tomato and zucchini.
• Fresh Thyme: 1 tablespoon, leaves stripped from stems. Provides a subtle, woodsy, and floral note that elevates the gratin.
• Black Pepper: ½ teaspoon, freshly ground. For a touch of spice and to enhance the other flavors.
• Gruyère Cheese: 1.5 cups, freshly grated. A nutty, slightly sweet, and salty cheese that melts beautifully, creating a creamy texture within the layers.
• Parmesan Cheese: ½ cup, freshly grated. Adds a sharp, salty, and umami-rich flavor, especially to the topping.
• Panko Breadcrumbs: ¾ cup. These Japanese-style breadcrumbs are lighter and flakier than traditional breadcrumbs, guaranteeing a superiorly crispy and golden topping.

Instructions

1. Prepare the Vegetables (The Anti-Soggy Step): Begin by preparing your primary vegetables to ensure your final gratin is tender and creamy, not watery. Slice the zucchini and tomatoes into uniform ¼-inch thick rounds. Consistency in thickness is key for even cooking. Place the zucchini slices in a colander set over a bowl or in the sink. Sprinkle them generously with 1 teaspoon of the kosher salt, tossing gently to coat. Let the zucchini sit for at least 30 minutes, or up to an hour. You will see beads of moisture form on the surface and drip into the bowl. This crucial step, known as disgorging, draws out a significant amount of excess water from the zucchini, which is the number one secret to preventing a soupy gratin. After 30-60 minutes, rinse the zucchini slices under cold water to remove the excess salt, then pat them thoroughly dry with a clean kitchen towel or paper towels. Be meticulous here; the drier the slices, the better the final texture.
2. Sauté the Aromatic Base: While the zucchini is resting, you can create the flavor foundation for your gratin. Heat 2 tablespoons of the olive oil in a large skillet or pan over medium heat. Once the oil shimmers, add the finely chopped yellow onion. Sauté the onion, stirring occasionally, for about 5-7 minutes, until it becomes soft, translucent, and slightly sweet. Add the minced garlic, dried oregano, and fresh thyme leaves to the skillet. Continue to cook for another 1-2 minutes, stirring constantly until the garlic is fragrant. Be careful not to let the garlic burn, as it will become bitter. This step blooms the flavors of the herbs and garlic, infusing the entire dish with their aroma. Remove the skillet from the heat and set it aside.
3. Preheat and Prepare the Baking Dish: Position a rack in the center of your oven and preheat it to 400°F (200°C). Take a 9×13 inch baking dish (or a similar 2.5 to 3-quart casserole dish) and rub the inside with the remaining 1 tablespoon of olive oil or a bit of butter. This prevents the gratin from sticking and adds another subtle layer of flavor.
4. Combine the Cheeses and Topping: In a medium-sized bowl, prepare your cheese and breadcrumb topping. Combine the ¾ cup of Panko breadcrumbs, the ½ cup of grated Parmesan cheese, and a pinch of black pepper. Drizzle with the remaining 1 tablespoon of olive oil and toss everything together with your fingers or a fork until the breadcrumbs are lightly and evenly coated. This mixture will become the irresistible crunchy, golden-brown crust. In a separate bowl, toss the 1.5 cups of grated Gruyère cheese with the remaining ½ teaspoon of kosher salt and ½ teaspoon of black pepper.
5. Assemble the Gratin Layers: Now for the fun part – assembling the gratin. Spread the cooked onion and garlic mixture evenly across the bottom of your prepared baking dish. This creates a savory bed for the vegetables. Begin arranging the vegetable slices on top of the onions. Start at one end of the dish and create overlapping rows, alternating between a slice of zucchini and a slice of tomato. Stand them up slightly on their edges, packed in snugly, creating a beautiful, scalloped pattern. This arrangement not only looks stunning but also helps with even cooking. Continue layering until the entire dish is filled. Don’t worry about perfection; a rustic look is part of the charm.
6. Add the Cheese and Bake: Sprinkle the seasoned Gruyère cheese evenly over the top of the arranged zucchini and tomatoes, tucking it between the slices where you can. The cheese will melt down into the vegetables, creating a rich, creamy sauce. Finally, sprinkle the Panko breadcrumb and Parmesan mixture evenly over the entire surface.
7. Bake to Golden Perfection: Place the baking dish on a baking sheet to catch any potential drips. Bake in the preheated 400°F (200°C) oven for 30 to 40 minutes. The gratin is done when the vegetables are tender (a knife should easily pierce a zucchini slice), the cheese is fully melted and bubbly, and the breadcrumb topping is a deep golden brown and crispy. If you find the topping is browning too quickly before the vegetables are cooked, you can loosely tent a piece of aluminum foil over the top for the last 10-15 minutes of baking.
8. Rest and Serve: This is a final, vital step. Remove the gratin from the oven and let it rest on a wire rack for at least 10-15 minutes before serving. This resting period allows the gratin to set up, making it easier to serve and allowing the flavors to meld together beautifully. Cutting into it too soon can result in a runnier consistency. Garnish with a sprinkle of fresh parsley or more fresh thyme leaves before serving, if desired.

Nutrition Facts

• Servings: 8 side-dish servings
• Calories per Serving: Approximately 280 kcal. This makes it a rich and satisfying side dish that can also be enjoyed as a lighter main course.
• Fat: 20g. Primarily from the olive oil and cheeses, providing a satisfying mouthfeel and helping you feel full.
• Carbohydrates: 15g. Mostly from the vegetables and a small amount from the breadcrumbs, making it relatively low in carbs.
• Protein: 12g. The cheese is the main contributor here, making this a surprisingly protein-rich vegetable dish.
• Fiber: 4g. The zucchini, tomatoes, and onion provide a good source of dietary fiber, which is important for digestive health.

Preparation Time

This dish requires a little bit of patience, but the results are well worth the effort. The total time is approximately 1 hour and 45 minutes, broken down as follows:

• Active Prep Time: 25 minutes (slicing vegetables, sautéing onions).
• Inactive Prep Time (Salting Zucchini): 30-60 minutes.
• Cook Time: 30-40 minutes.
• Resting Time: 10-15 minutes.

How to Serve

This Zucchini Tomato Gratin is incredibly versatile. It can be the star of a vegetarian meal or a stunning supporting actor to a variety of main courses. Here are some wonderful ways to serve it:

• As a Hearty Vegetarian Main Course:
  • Serve generous portions alongside a loaf of crusty, artisanal bread for sopping up the delicious, cheesy juices.
  • Pair it with a simple, crisp green salad dressed with a sharp lemon vinaigrette to cut through the richness of the gratin.
  • Accompany it with a scoop of quinoa or a fluffy couscous salad for a complete and balanced meal.
• As an Elegant Side Dish:
  • With Poultry: It’s a perfect companion to a simple roast chicken or turkey breast. The savory, herbaceous flavors of the gratin complement the poultry beautifully.
  • With Beef: Serve it alongside a grilled steak or a slow-cooked beef roast. The acidity from the tomatoes helps balance the richness of the meat.
  • With Fish: It pairs wonderfully with a flaky white fish like cod or halibut, whether it’s baked, pan-seared, or grilled.
  • For a Barbecue: Bring this gratin to your next cookout. It’s a sophisticated alternative to traditional side dishes and pairs well with grilled sausages, burgers, and chicken.

Additional Tips

1. Don’t Skip the Salting: It might seem like a tedious extra step, but salting and draining the zucchini is the most important technique for achieving a perfect gratin texture. Zucchini is over 90% water, and skipping this step will almost certainly result in a soupy, watery dish.
2. Cheese Choice Matters: While Gruyère is the classic choice for its superior melting quality and nutty flavor, feel free to experiment. A mix of sharp white cheddar and mozzarella would be delicious, or try fontina, provolone, or even a smoked gouda for a different flavor profile. Always grate your own cheese from a block for the best meltability; pre-shredded cheeses often contain anti-caking agents that can make the sauce gritty.
3. Uniform Slices for Even Cooking: Use a mandoline slicer if you have one for perfectly uniform ¼-inch slices of both the zucchini and tomato. This not only creates a visually stunning presentation but, more importantly, ensures that all the vegetables cook at the same rate.
4. The Breadcrumb Boost: For an even crunchier and more flavorful topping, try toasting the Panko breadcrumbs in a dry skillet over medium heat for 3-5 minutes until lightly golden before mixing them with the Parmesan and olive oil. This pre-toasting deepens their nutty flavor.
5. Let It Rest, Seriously: The 10-15 minute resting period after baking is non-negotiable. It allows the molten cheese and vegetable juices to cool slightly and set. This transforms it from a soupy collection of vegetables into a cohesive, sliceable gratin.
6. Herbaceous Elevation: While dried oregano works well, using all fresh herbs will take your gratin to the next level. If you have fresh oregano, use about 1 tablespoon, finely chopped. Fresh basil, stirred in at the very end or used as a garnish, would also be a fantastic addition.
7. Garlic Lover’s Dream: If you are a true garlic aficionado, you can enhance the garlic flavor by rubbing a cut clove of garlic all over the inside of your baking dish before you oil it. This imparts a subtle, fragrant garlic essence into the entire bottom layer of the gratin.
8. Baking Dish Basics: A ceramic or stoneware baking dish is ideal for gratins. These materials retain and distribute heat evenly, which helps cook the vegetables through while creating a beautifully browned crust. A glass dish will also work, but you may need to reduce the oven temperature by 25°F as glass heats up faster.

FAQ Section

1. Q: Why did my Zucchini Tomato Gratin turn out watery and soupy?
A: This is the most common issue with zucchini gratins. The culprit is almost always excess moisture from the vegetables. To prevent this, you must follow the first instruction meticulously: salt the zucchini slices and let them drain for at least 30 minutes. Patting them completely dry afterward is equally important. Using firmer, less-juicy Roma tomatoes can also help.

2. Q: Can I make this gratin ahead of time?
A: Yes, you can assemble the entire gratin up to 24 hours in advance. Prepare the recipe through step 6 (just before baking), cover the dish tightly with plastic wrap or foil, and refrigerate. When ready to bake, remove it from the refrigerator for 30 minutes to come to room temperature, then bake as directed, possibly adding 5-10 minutes to the total baking time. Note that the breadcrumb topping will be best if added just before baking.

3. Q: How do I store and reheat leftovers?
A: Store any leftover gratin in an airtight container in the refrigerator for up to 3-4 days. The best way to reheat it is in an oven or toaster oven at 350°F (175°C) for 15-20 minutes, or until warmed through. This method helps to re-crisp the topping. Microwaving will work in a pinch, but the topping will become soft.

4. Q: Can I freeze Zucchini Tomato Gratin?
A: While you can freeze it, the texture will be compromised upon thawing. Zucchini and tomatoes have a high water content, and they tend to become very soft and mushy after being frozen and reheated. The cheesy sauce may also separate. For best results, this dish is best enjoyed fresh or refrigerated and eaten within a few days.

5. Q: What are some good variations for this recipe?
A: This recipe is a fantastic template for creativity! You can add a layer of thinly sliced yellow squash or eggplant along with the zucchini. Incorporating a layer of sautéed mushrooms or spinach (be sure to squeeze it very dry) into the onion base adds another dimension of flavor. For a touch of heat, add ¼ to ½ teaspoon of red pepper flakes along with the garlic.

6. Q: Can I make this recipe vegan or dairy-free?
A: Absolutely. To make it dairy-free and vegan, use your favorite brand of vegan shredded cheese that melts well (a blend of vegan mozzarella and parmesan style works great). Ensure your breadcrumbs are vegan (most Panko brands are). You will achieve a similar comforting, bubbly result.

7. Q: What is the difference between a gratin and a casserole?
A: The terms are often used interchangeably, but there is a technical difference. A “gratin” (from the French word for “crust”) is defined by its topping. A true gratin always has a browned crust, typically made from breadcrumbs, cheese, butter, or a combination. A casserole is a more general term for any dish cooked and served in a single deep dish. So, while this dish is a type of casserole, calling it a gratin specifically highlights its delicious, crunchy topping.

8. Q: My breadcrumb topping burned before the vegetables were cooked. What did I do wrong?
A: This can happen if your oven has hot spots or if the topping is too close to the heating element. To prevent this, make sure your oven rack is in the center position. If you notice the topping browning too quickly partway through baking, simply tent a piece of aluminum foil loosely over the top of the dish. This deflects the direct heat from the topping while allowing the vegetables underneath to continue cooking through.

Print