To prepare sauce, combine first 4 ingredients in a small saucepan over low heat, stirring well with a whisk. Cook until jelly melts.
To prepare sandwiches, combine egg substitute, milk, salt, and pepper in a shallow dish.
Place one slice each of the turkey, ham, and cheese on each of 4 bread slices. Top with remaining bread slices. Dip both sides of each sandwich into the egg substitute mixture. Place sandwiches in a large nonstick skillet coated with cooking spray over medium-high heat. Reduce heat to medium; cook for 3 minutes on each side or until sandwiches are golden. Sandwiches can also be cooked in a pannini press.
Sprinkle sandwiches with powdered sugar. Serve sandwiches with sauce.