Melt butter and peanut butter in a large saucepan over low heat

Stir in chips until melted

Cool until you can hold your hand on the bottom of the pot (to quicken process, stir while holding pan in cold water until cool enough)

Add marshmallows and stir until all are coated

Pack down in a 9x9 inch pan that has been lined with wax paper

Refrigerate until ready to serve and cut into squares