Preheat oven to 325° F. In large skillet, cook sausage over medium-high heat, stirring frequently, until thoroughly cooked and no longer pink. In large mixing bowl, combine eggs, milk, mustard and salt; stir well. Distribute half the bread evenly in a buttered 9- x 13- x 2-inch baking dish. Sprinkle with half the pepper, half the cheese, half the sausage and half of each optional ingredient. Repeat layering using remaining bread, pepper, cheese, sausage and optional ingredients. Pour egg mixture evenly over casserole. Bake uncovered for 55 to 60 minutes, or until eggs are set. Tent with foil if top begins to brown too quickly.
Note: Casserole may be assembled ahead and refrigerated up to 12 hours before baking.