Spray a 9-by-12 inch glass dish with vegetable cooking spray. Line dish with one layer of white bread. Sprinkle half of the three cheeses over the bread. Add a second layer of bread and the remainder of the cheese.
In a medium-size bowel, mix the eggs, milk, melted butter, and dry mustard well. Pour egg mixture over the bread and cheese. Cover the dish with plastic wrap and refrigerate overnight.
In the morning, remove plastic wrap, and bake in a preheated 350-degree oven for 45 minutes to 1 hour. Let it sit for 1 to 2 minutes before cutting into squares. The layered paradise needs to be served immediately.