In the bowl of a stand mixer fitted with a paddle attachment, beat butter, peanut butter, and brown sugar until light and fluffy. Add cream cheese and beat until mixture is smooth, scraping down the sides as necessarily. Slowly beat in powdered sugar, vanilla, and salt. Use a rubber spatula to fold in about ¾ of the chopped Hershey's bars and ¾ of the marshmallow bits.

Sprinkle the remaining chocolate and marshmallows on top. Chill until ready to serve. Serve with graham crackers.