Bologna Strata

12 slices firm white bread, crusts removed
1/2 lb. sliced American cheese
2 1/2 cups milk
1 tablespoon minced onion
1/4 teaspoon pepper
1/2 lb. sliced bologna
4 eggs
1 teaspoon mustard
1 teaspoon salt

Grease a 13x9-inch baking dish. Arrange 6 slices bread in one layer across the bottom of the baking dish. Cover with bologna slices, cheese slices, and top with remaining 6 slices bread. Beat eggs well. Add remaining ingredients and beat again. Pour egg mixture over the layers in baking dish. Let stand 1 hour or refrigerate overnight. Bake at (350F) uncovered for about 50 minutes until puffed and lightly browned.