Coat a 9 x 13-inch baking dish with cooking spray.
Arrange the slices of bread in a single layer in the bottom of the dish.
In a glass measuring cup, melt the butter or margarine in the microwave oven for 40 seconds on high.
Drizzle over the bread.
Sprinkle the cheese evenly over the bread.
In a large mixing bowl, combine the milk and the eggs, mixing well.
Pour over the cheese.
Cover with plastic wrap and refrigerate at least 8 hours or overnight.
When ready to bake, uncover and place in a cold oven. Then set to 350° F. This is necessary because the dish is coming out cold from the refrigerator and might crack if placed in a preheated oven.
Bake for 50 minutes.
The casserole will be puffy and lightly browned.