Preheat the oven to 350 F. In a large bowl, combine peanut butter with sugar and egg until smooth. Use a cookie scoop to place the cookie dough onto a large ungreased baking sheet at least 2-inches apart.
Bake for 10-12 minutes. Remove half of the cookies from the baking sheet. Place one marshmallow and some chocolate chips on each peanut butter cookie on the baking sheet.
Bake for 2-3 minutes. Remove from the oven, and sandwich with the remaining half of cookies.