Assemble casserole 12 to 24 hours before baking and refrigerate.
Generously butter 9x13 inch glass baking dish. Arrange bread cubes (8 slices, if using Pepperidge Farm) on bottom. Sprinkle with meat, then with cheese. Beat together milk, eggs, mustard, onion powder, salt, and pepper. Before baking, sprinkle with paprika. Bake at 300 degrees for 1 hour Make 12 servings.