Remove crust and cube bread. Chop onions. Put all in a deep, greased 9 x 3 casserole dish. Beat eggs; add milk, salt, mustard, and cheese. Pour over bread mixture and let stand (in refrigerator) overnight.
Before baking, cover with soup, cream, mushrooms, and broccoli. Bake at 300 degrees for 1 1/2 hours; let stand 10 to 15 minutes. Yield: approximately 8 main servings.