Place croutons in a 9 x 13 inch buttered pan. Place cheese on top of croutons. Fry sausage, drain and put on top of cheese. (Other types of meat can be substituted for the sausage.) Beat eggs, mustard and 2 1/2 cups of milk together. pour over the meat. Cover and refrigerate overnight. Next morning, mix 1/2 cup of milk with mushroom soup and pour over top of casserole. Bake at 300 for 1 1/2 hours.
Makes 6 - 8 servings.