1Make the night before:
Place croutons in bottom of a greased 9 x 13 pan. Mix 2 cups cheese, mushrooms and crumbled sausage in a bowl. Mix well.
spread over croutons.
2Combine eggs, milk, soup and mustard in a bowl. Mix well. Pour egg mixture over ingredients in pan, DO NOT STIR. Cover with foil, regrigerate, overnight.
3Bake uncovered at 350 degrees for 1 hour 15 minutes or until set. Cheese will make it oist. Take out of oven, sprinkle with 1 cup remaining grated cheese. Let sit for at least 15 to 20 minutes until cheese on top melts. Serve.