Preheat your oven to 350 degrees.

In a large bowl, combine the cake mix & melted butter (let the butter cool just a bit before adding it to the cake mix). The mixture will be crumbly.

Reserve 1 & 1/2 cups of the mixture for the topping. Pat the remaining mixture into the bottom of an ungreased 12x8x1 baking dish*.

In a small bowl, combine the peanut butter & the marshmallow creme. Spread the peanut butter mixture evenly over the crumb mixture in the dish. Sprinkle the reserved cake mix over the peanut butter layer.

Bake for 18 - 20 minutes. Let cool & then cut into bars.