Use day-old bread for best texture as it soaks up the egg mixture without becoming mushy. Let the casserole rest after baking to firm up and make slicing neater. Feel free to swap sausage for plant-based alternatives or add vegetables like spinach, bell peppers, or mushrooms for extra flavor and nutrition. For a creamier casserole, substitute half the milk with heavy cream or creamy plant-based milk. To save time, cook and crumble sausage the night before. Use sharp cheddar for tanginess or mild cheese for subtle taste.