Heat oven to 325°. Layer 6 bread slices, cheese, broccoli and ham in a lightly greased 9x13-inch baking pan. Place remaining bread on top. Mix eggs, milk, onion, salt and dry mustard; pour over layers. Let stand, covered, in refrigerator for six hours or overnight. Remove from refrigerator 30 minutes before baking. Bake for 45 to 55 minutes or until set and light brown. Let stand for 10 minutes before serving. Yields 8 servings.