Grease and flour a 15 x 11-inch jellyroll pan. Preheat oven to 350°.

1st Layer: Prepare cake as directed on box, using the water, oil and eggs. Pour cake mixture into pan. Bake 20 to 22 minutes, or until a toothpick inserted comes out clean. Cool completely.

2nd Layer: In a saucepan, bring sugar and 1/2 cup milk to a boil. Boil 3 minutes. Add peanut butter and marshmallow creme; mix well. Quickly pour on top of the cooled cake. Spread evenly. Cool completely.

3rd Layer: In a medium saucepan, melt butter, cocoa and 1/3 cup milk together. Bring to a boil. Remove from heat and add confectioners' sugar and vanilla. Stir completely. Pour icing on top of the cooled peanut butter layer. Cool completely before cutting.