Preheat oven to 350° F. Grease a 9x13" baking pan.

In a large bowl, using a wooden spoon, mix together the cake mix, melted butter, milk, brown sugar, and eggs until blended.

Fold in the peanut butter chips.

Press into prepared pan.

Bake 20 minutes.

Once the crust is baked, remove from oven. Leave the oven on.

Place the peanut butter in a small microwaveable bowl and microwave for 15-20 seconds, until melted.

Drizzle the peanut butter over the partially baked bars.

Sprinkle the marshmallows over the peanut butter.

Put the pan back in the oven and bake for an additional 10-12 minutes, until marshmallows are puffed up and golden.

Cool in pan for 10 minutes before removing to wire rack to cool completely.

Cut into bars and serve with a glass of milk.