Cut bacon in small pieces and fry until crisp. Cut bread slices in cubes and place in greased 2 quart casserole dish Cube or shred cheese and put on top of bread. In blender or mixing bowl beat eggs, milk, salt and mustard. Pour over bread and cheese. Sprinkle bacon pieces over top. Cover and refrigerate overnight. Bake, covered, at 350 degrees for 50-60 minutes or until puffed up.