Put slice of cheese on each piece of bread, then place asparagus evenly on top of cheese. Top each with another slice of bread.
Mix eggs, milk, salt, pepper and mustard and pour over bread. Let refrigerate overnight.
Sprinkle top with additional grated cheese and bake at 350F degrees for 45 to 50 minutes or until custard is set, knife comes out clean when inserted.
Yield: 4 servings.