With end of round handle of wooden spoon, make deep, 1/2-inch-wide indentation in center of each cupcake, not quite to the bottom (wiggle end of spoon in cupcake to make opening large enough). In small bowl, mix 1 cup vanilla frosting and the marshmallow creme. Spoon into small resealable food-storage plastic bag. Cut 3/8-inch tip off 1 bottom corner of bag. Insert tip of bag into each cupcake and squeeze bag to fill.