In a medium saucepan, melt the butter, peanut butter and chocolate chips over medium-high heat. Remove from the heat and set aside to cool slightly so that you don’t melt the marshmallows. Stir in the marshmallows and cereal and spread into a parchment-lined 8×8-inch pan. Refrigerate until firm and cut into squares.

If you’re into the peanut butter & cereal bar combination, you’ll probably love these Cheerio Bars, too.