Unlike many recipes, this egg casserole is made without bread. And since you can make it the night before, it’s perfect for holiday brunches or make-ahead family breakfasts!
In a large non-stick skillet over medium heat, cook sausage, onions, mushrooms, and garlic until sausage is no longer pink and mushrooms have given off some of their liquid, about 10 minutes.
In a medium bowl, combine eggs, milk, parsley, salt, basil, and pepper. Whisk thoroughly to combine, then add remaining 1 cup of cheese and whisk again.
You can make this in the morning and refrigerate until baking, or prep it in the afternoon and then cook it immediately, for a fun "breakfast for dinner" option.