In a large skillet, heat over medium heat and add 1 pound of breakfast sausage, breaking it into smaller pieces. Cook for about 8-10 minutes until the sausage is browned and cooked through, stirring occasionally. Once browned, add 1 tablespoon of dried minced onion, cooking for an additional 2-3 minutes until softened and fragrant.

After cooking, carefully drain the excess fat from the skillet to prevent a greasy casserole. Remove the sausage and onion mixture from the heat and set it aside in a bowl, allowing it to cool slightly while you prepare the egg mixture.

In a large mixing bowl, crack 12 large eggs and whisk until smooth. Then, pour in 3/4 cup of whole milk along with 1 teaspoon of salt and 1/4 teaspoon of ground black pepper. Whisk the ingredients together until combined.

Preheat your oven to 350°F (175°C). While the oven heats, grease a 9x13 inch casserole dish generously with cooking spray or butter.

Spread 3/4 of the sausage and onion mixture evenly across the bottom of the greased casserole dish. Then, sprinkle half of the 1 cup of shredded sharp cheddar cheese on top.

Carefully pour the egg mixture over the layers in the casserole dish, ensuring it evenly covers the sausage and cheese.

Place the casserole in the preheated oven and bake for about 30 minutes. After this time, the eggs should be mostly set but may still have a slight jiggle in the center.

After 30 minutes, carefully remove the casserole from the oven. Sprinkle the remaining sausage mixture and the rest of the cheddar cheese on top. Return the dish to the oven and bake for an additional 10-15 minutes until the cheese is melted and bubbly.

Once the cheese has melted and the casserole is bubbling, remove it from the oven. Allow it to cool slightly for about 5 minutes before slicing it into squares.