Preheat the oven to 350 degrees Fahrenheit.
In a medium sized mixing bowl, combine the flour and baking powder. Remember to measure the flour using the scoop & level method which is explained above.
In a stand mixer, combine the cold, cubed butter with the granulated sugar and brown sugar. Mix with the paddle attachment until creamed together.
Add the egg and vanilla extract to the mixing bowl and mix until combined.
Slowly add in the flour mixture until the dough is almost together. It should still have some sticking to the side of the bowl.
Pour in the marshmallow bits and chocolate chips, then mix on low or stir until the dough forms a ball.
Roll the cookies out to 3/8" onto a floured surface. Cut the cookies using a cookie cutter and bake on a prepared cookie sheet for 8-10 minutes or until the top of the cookie doesn't look wet. This recipe works best with a metal cookie cutter to cut through the s'mores ingredients but a plastic one will work as well.