In a medium saucepan on low heat, combine the flour, sugar, and milk, stirring constantly. It will take a while to start to boil cooking on low but once it starts, the pudding will thicken up really quick. Cook for one minute after the mixture has started to boil, stirring continually.
In a mixing bowl, beat the butter until creamy. Pour in the cooled melted Reese’s Peanut Butter Cups and beat until the butter is fluffy.