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.
Throughout cooking, stir to crumble sausage and break up mushrooms. (You can leave the mushrooms in larger slices or break them into almost unnoticeable little pieces as you crumble the sausage.)