For a richer flavor, try using a combination of cheddar and Gruyere cheese. Add a dash of hot sauce or a pinch of red pepper flakes to the egg mixture for a little kick. Feel free to add other vegetables to the sausage mixture, such as diced onions, bell peppers, or mushrooms. This casserole can be assembled ahead of time and stored in the refrigerator overnight. Just add a few extra minutes to the baking time if baking from cold.