Grilled Cheese Brunch Bake

Preheat oven to 350 degrees F (175 degrees C). Grease a 9×13-inch casserole dish with cooking spray.

Spread an even layer of mayonnaise on one side of each slice of bread. Place 6 slices of bread mayonnaise-side down in a single layer at the bottom of the casserole dish.

Bake in the preheated oven until lightly toasted, about 5 minutes. Remove from oven and top each slice of bread with 1 slice of Cheddar cheese. Cover with 6 more slices of bread, mayonnaise-side up.

Bake in the preheated oven until bread is lightly toasted, about 5 minutes.

Sprinkle 1/4 of the shredded Cheddar cheese on top. Arrange slices of ham on top; cover with another 1/4 of the shredded Cheddar cheese. Repeat with bacon slices, covering with another 1/4 of the shredded Cheddar cheese. Arrange last 6 slices of bread, mayonnaise-side up, on top.

Whisk eggs, milk, salt, and black pepper together in a large bowl. Pour evenly over bread in the casserole dish. Sprinkle remaining 1/4 cup shredded Cheddar cheese on top. Cover with aluminum foil.

Bake in the preheated oven until set, about 30 minutes.

Remove aluminum foil and continue baking until cheese is bubbly and golden, 5 to 10 minutes more.