Place 2 1/2 cups herb croutons on bottom of buttered 9 x 13 pan. Top with 2 cups shredded sharp cheese. Brown and drain 2 pounds sausage. Layer sausage over cheese. Beat 8 eggs with 3/4 teaspoon dry mustard and 2 1/2 cups milk. Pour over crouton-cheese-sausage and refrigerate overnight. Sprinkle with parsley. Dilute 1 can of mushroom soup with 1/2 cup milk. Pour over mixture and bake at 350 degrees for 1 1/2 hours.