Yield: 24 servings
In a large bowl, toss bread, ham and cheese; divide between two greased 13 x 9 x 2- inch baking pans.
In a skillet, saute onion in butter until tender; transfer to bowl. Add eggs, milk and mustard; whisk together until well blended. Pour over bread mixture. Cover and refrigerate overnight.
Remove from the refrigerator 30 minutes before baking. Bake, uncovered, at 350 degrees F for 55 to 65 minutes or until a knife inserted near the center comes out clean. Serve immediately.
Please note that some ingredients and brands may not be available in every store.