Preheat the oven to 350°F (177°C). Spray 8×11.5 (or 9×13) baking pan with cooking spray.
Spread leftover stuffing in the baking pan in an even layer.
In a large bowl, whisk together eggs, milk and half of the cheese.
Pour the egg mixture over the stuffing and top with remaining cheese.
Bake, uncovered, for 40-45 minutes, or until the eggs are fully cooked.
Notes
Note 1: You can use any kind of stuffing, but I prefer a sausage stuffing, as it makes a heartier breakfast.Note 2: You can use any kind of milk, I use whole milk or 2%. You can also use chicken broth, if you'd like.Make-Ahead Instructions: 1. You can prepare the casserole through step 6. Cover and refrigerate overnight and bake it in the morning. Bring it to room temperature before baking, about 30 minutes on the counter. 2. Or you can bake the casserole the night before and reheat it in the morning. This casserole reheats beautifully.Instant Pot Breakfast Casserole: You can also make a smaller batch in an Instant Pot.