Preheat oven to 350F. Line an 9x9 inch pan with parchment or spray with baking spray.

Beat together the cake mix, egg, and ¼ cup of butter. Press into the prepared pan and bake for about 10 - 12 minutes until set.

Meanwhile, over low heat, melt the remaining ½ cup butter, peanut butter chips, and light corn syrup. Stir frequently until smooth. Remove from heat and stir in vanilla. Add peanuts and Rice Krispies and stir gently until everything is coated in the peanut butter mixture.

When the crust is done baking, top with marshmallows. Return to the oven for about 3 minutes or until marshmallows are puffed. Remove from oven and top with peanut mixture. Refrigerate until set. Cut into squares and enjoy!