Preheat the oven to 350°F (175°C).
In a large skillet over medium heat, cook the breakfast sausage until browned and fully cooked, breaking it up into crumbles as it cooks (about 7-10 minutes).
Drain the excess grease and set the sausage aside.
In a large mixing bowl, crack the 12 eggs and add ½ cup of milk.
Season with salt and pepper to taste and whisk until fully combined and slightly frothy.
Grease a 9×13-inch baking dish with nonstick cooking spray or butter.
Spread the thawed hash browns evenly across the bottom of the dish.
Sprinkle the cooked sausage evenly over the hash browns.
Add a layer of shredded cheddar cheese, using about 1 cup.
Pour the egg mixture over the sausage and cheese, ensuring it covers everything evenly.
Sprinkle the remaining 1 cup of shredded cheddar cheese on top.
Cover the baking dish with aluminum foil and bake for 30 minutes.
Remove the foil and continue baking for an additional 20 minutes, or until the eggs are set and the top is golden and bubbly.
Let the casserole rest for about 5 minutes before cutting into squares and serve warm.
