Preheat oven to 375F and line baking sheets with parchment paper.
In your mixer, cream together shortening, brown sugar, white sugar, and peanut butter. Add in eggs, one at a time, stirring well after each addition. Add in vanilla and stir.
In a separate bowl, combine flour, baking powder, and salt.
Gradually, with mixer on low-medium, add the dry mixture to the wet until combined.
Stir in marshmallows and chocolate chips.
Spoon cookie dough by 1 ½" portions onto prepared cookie sheet. Using the tines of a fork, gently press to create a criss-cross pattern on cookies and slightly flatten them.
Bake for 7 minutes. Allow cookies to cool on baking sheet for several minutes before transferring to wire rack to cool completely.