Grease 9" x 13" metal pan. Partially cook broccoli; drain well on paper towels. Cut off crusts and cube bread, spread in pan. Layer ham, then broccoli. Sprinkle onion then cheese.
In large bowl, combine beaten eggs, milk, salt and mustard. Pour over bread. Cover, refrigerate 6 hours or overnight.
Heat oven to 325 degrees. Bake uncovered for 1 1/4 hours until inserted knife comes out clean. Let stand 10 minutes before serving. Serves 8-12