In a medium shallow bowl, beat together egg, milk, salt and pepper. Set aside.
In a skillet, over medium heat, melt butter.
Spread mustard on one slice of bread, top with turkey slices, then cheese slices.
Spoon cranberry sauce over cheese, top with remaining piece of bread.
Carefully dip sandwich into egg mixture, saturating both sides of bread.
Brown sandwich in melted butter over medium heat until golden brown on both sides.