Follow these steps carefully for the perfect Creamy Spinach Rice Bake:

1. Preheat and Prepare: Preheat your oven to 375°F (190°C). Lightly grease a 9×13 inch baking dish (or a similar 2.5-3 quart casserole dish) with butter or non-stick spray.
2. Sauté Aromatics: Place a large oven-safe pot or Dutch oven over medium heat. Add the olive oil and butter. Once the butter is melted, add the finely chopped onion. Sauté for 5-7 minutes, stirring occasionally, until the onion is softened and translucent. Add the minced garlic and cook for another minute until fragrant, being careful not to burn it.
3. Toast the Rice: Add the uncooked long-grain white rice to the pot with the onions and garlic. Stir well to coat the rice grains with the oil and butter mixture. Toast the rice for 1-2 minutes, stirring constantly, until the edges of the grains look slightly translucent. This step helps the rice grains remain distinct and absorb liquid evenly.
4. Add Liquid and Simmer: Pour in the vegetable broth (or chicken broth). Add the salt, black pepper, nutmeg (if using), and red pepper flakes (if using). Stir everything together well. Bring the mixture to a simmer.
5. Initial Rice Cooking: Once simmering, cover the pot tightly, reduce the heat to low, and let the rice cook for 15 minutes. It won’t be fully cooked at this stage, but it will have absorbed a good portion of the liquid. This pre-cooking step ensures the rice finishes perfectly in the oven without becoming mushy or remaining hard.
6. Incorporate Creamy Elements: Remove the pot from the heat. Add the thawed and thoroughly squeezed dry spinach, the cubed softened cream cheese, heavy cream (or half-and-half), and half of the Parmesan cheese (¼ cup). Stir gently but thoroughly until the cream cheese melts and combines with the residual heat and liquid to form a creamy sauce that coats the rice and spinach evenly. It might look a little loose at this stage, but it will thicken during baking.
7. Add Most of the Cheese: Stir in half of the shredded mozzarella cheese (or your chosen melting cheese – ½ cup). Mix until it’s just combined.
8. Transfer to Baking Dish: Carefully pour the rice mixture into the prepared baking dish, spreading it into an even layer. If your pot is not oven-safe, transfer the mixture now. If you used an oven-safe Dutch oven, you can bake it directly in that (ensure it’s not too full).
9. Top and Bake: Sprinkle the remaining shredded mozzarella (½ cup) and the remaining Parmesan cheese (¼ cup) evenly over the top of the rice mixture.
10. Bake: Place the baking dish in the preheated oven. Bake for 20-25 minutes, or until the top is golden brown and bubbly, and the sauce has thickened further. The edges should be visibly bubbling.
11. Rest Before Serving: Remove the Creamy Spinach Rice Bake from the oven. Let it rest for 5-10 minutes before serving. This allows the sauce to set slightly, making it easier to serve and preventing it from being too runny. It also allows the flavours to meld beautifully.
12. Serve: Garnish with fresh parsley or chives if desired, and serve hot.