Preheat oven to 350°F. Lightly grease a 9x13 baking dish with cooking spray.
Mix the cake mix, egg and ¼ cup melted butter. Press into the greased pan. Bake for 12 minutes.
Arrange the marshmallows on top of the hot crust. Return to oven for about 3 minutes. The marshmallows should be puffy and soft.
Melt the peanut butter chips, corn syrup and ½ cup butter in the microwave using 30 second intervals. Stir in the vanilla. Add the peanuts and stir. Add the Rice Krispies, and mix well.
Pour the peanut mixture over marshmallows and use a spatula to spread it evenly to the edges.
Refrigerate to allow the topping to set and cool. Cut into squares and serve.