Preheat oven to 350 Degrees F.

Prepare a 9 X 13 baking pan by lining bottom and sides with parchment paper and spraying with baking spray.

Combine cake mix, 1/3 cup of butter, and egg. Mix well until it forms a dough.

Place dough into prepared pan and press out dough into an even layer covering the entire bottom of the pan. Hands damped with water can be used to spread dough.

Place pan into preheated 350 Degree F oven and bake for 15 to 18 minutes or until the top is lightly browned.

Remove from oven, turn off the oven and immediately place mini marshmallows on top of the hot crust, moving marshmallows as necessary to cover all of the crust and avoid marshmallow piles.

Allow marshmallows to soften and flatten. Crust topped with marshmallows can be placed back into the cooling oven for 3 to 5 minutes if marshmallows are not softening.

While marshmallows are softening, begin making salted peanut topping by place corn syrup and 1/4 cup of butter into a medium saucepan and cooking over medium-low heat until butter is melted.

Remove from heat and add vanilla and peanut butter chips, mixing until all peanut butter chips are melted.

Add salted peanuts and crispy rice cereal, mix until peanuts and cereal are coated with peanut butter mixture.

Place small spoons of hot mixture over softened marshmallows.

Spread out with a knife, it will be thick and get thicker as it cools. Gently continue nudging peanuts to fill in areas of exposed marshmallows. These areas will smooth themselves out as the dish cools.

Allow topping to cool and set slightly.

Remove the pan of bars from the pan and place on a cooling rack.

Peel back the parchment paper from the sides of the bars before the bars cool completely. This may require a sharp knife in some areas.

Once cooled completely, cut into 24 bars.