Preheat your oven to 350 degrees Fahrenheit. Grease a 9×13 inch baking dish.
Spread the thawed hash browns evenly across the bottom of the prepared baking dish.
Sprinkle the cooked sausage and half of the combined cheeses over the hash browns.
In a large bowl, whisk together the eggs, milk, salt, pepper, and garlic powder until well combined.
Pour the egg mixture evenly over the sausage and hash brown layers.
Top with the remaining half of the shredded cheeses.
Cover the dish tightly with aluminum foil.
Bake for 30 minutes covered. Remove the foil and bake for an additional 15 to 20 minutes, or until the eggs are set and the top is lightly golden brown.
Let the cheesy egg casserole rest for 10 minutes before slicing and serving.
Notes
For a make-ahead breakfast casserole, assemble the entire dish (steps 1 through 5), cover tightly, and refrigerate for up to 24 hours. When ready to bake, add 10 minutes to the covered baking time.
You can substitute turkey sausage or bacon for the breakfast sausage for a different flavor profile.
This savory breakfast casserole freezes well. Cool completely, wrap tightly, and freeze for up to three months. Thaw overnight in the refrigerator before reheating.