1. In a large bowl, beat the cake mix, egg and butter on low speed until combined. Press into a 13-in. x 9-in. baking pan coated with cooking spray.
2. In a another large bowl, beat cream cheese and pumpkin until smooth. Add the butter, eggs, egg whites and vanilla; beat on low until combined. Add the confectioners' sugar cinnamon and nutmeg; mix well. Pour over crust.
3. Bake at 350 degrees for 45-50 minutes or until edges are golden brown. Cool completely on a wire rack. Chill until serving. Sprinkle with additional confectioners' sugar if desired. Refrigerate leftovers.