Peanut Butter & Marshmallow Brownies

I was so surprised to find this recipe in Grandma's collection.  It uses jarred marshmallow cream.  Such a modern day ingredient.

1 box of brownie mix (I like Duncan Hines Fudgy brownies)
1 jar (7 1/2 oz) marshmallow cream
1 cup prepared creamy chocolate frosting
1 cup creamy peanut butter

Prepare and bake brownie mix according to package directions in a 13 x 9" baking pan.  Evenly drop marshmallow cream onto cooled brownies and spread evenly with a spoon.  Heat the frosting in a small saucepan until it is melted and smooth.  Heat the peanut butter in another saucepan until it is melted and smooth.  Pour melted frosting and then melted peanut butter over marshmallow cream and swirl with butter knife to marble.  Let cool completely on wire rack.