Preheat oven to 400. Prepare bottom only of a 9" pie pan with cooking spray and flour; set aside. In a mixing bowl, combine bread mix, sour cream, milk, one egg, and the yolk. Mix until moistened. Pour into prepared pan; set aside. Meanwhile, in a small bowl, beat reserved egg white. Brush over top batter in pan. Sprinkle top evenly with sugar. Bake for 25 minutes, or until golden brown.