Preheat oven to 350 degrees F (175 degrees C).

Coat a 13x9 inch baking pan with cooking spray.

In a large bowl, combine yellow cake mix, egg, and melted butter.

Beat on low speed until combined.

Press the mixture into the prepared baking pan to form the crust.

In another large bowl, beat cream cheese and pumpkin until smooth.

Add melted butter, eggs, egg whites, and vanilla extract to the cream cheese mixture.

Beat on low speed until combined.

Add confectioners' sugar, cinnamon, and nutmeg.

Mix well until fully incorporated.

Pour the pumpkin filling over the cake crust.

Bake in the preheated oven for 45-50 minutes, or until the edges are golden brown.

Cool completely on a wire rack.

Chill until serving.

Sprinkle with additional confectioners' sugar before serving, if desired.

Refrigerate any leftovers.