Creating this Cheesy Potato Breakfast Casserole is as easy as it is delicious. Follow these step-by-step instructions:

1. Preheat the oven to 350°F (175°C). Spray a 9×13 inch casserole dish with non-stick spray to prevent sticking.
2. Cook the sausage in a skillet over medium heat until browned and cooked through. Remove the sausage from the skillet and set aside.
3. Sauté the onion: In the same skillet (using the sausage grease), sauté the chopped onion until it becomes soft and translucent.
4. Mix the ingredients: In a large bowl, combine the cooked sausage, sautéed onion, eggs, milk, frozen hash browns, and half of the grated cheddar cheese. Season generously with salt and pepper to taste.
5. Assemble the casserole: Pour the mixture into the prepared casserole dish. Spread it out evenly, then top with the remaining cheddar cheese.
6. Bake: Place the casserole in the preheated oven and bake for 35 minutes, or until the eggs are set and the top is golden brown.
7. Rest and serve: Allow the casserole to rest for 15 minutes before serving. This will make it easier to slice and serve while ensuring that the flavors meld together perfectly.