Smear some mustard on two slices of bread. Top each with three slices of ham, one slice of cheese, and a slice of bread. Whisk together the egg, milk, cinnamon, and vanilla in a shallow pan. Dip each sandwich into the egg mixture, making sure to evenly coat both sides. Add the butter to a large skillet set over medium heat. When melted, add the sandwiches and cook on both sides until browned. Sprinkle with the sugar, and serve with the strawberry jam.
