Preheat oven to 350° and line 2 baking sheets with parchment paper. Break nine of the graham cracker sheets in half and place nine squares evenly apart on each baking sheet.
In the bowl of a stand mixer or using a handheld mixer, cream together butter and sugar on medium-low speed for 3 minutes.
Mix in the egg and vanilla.
In a small bowl, combine flour, salt and baking soda. Gently mix into dough on low speed until just incorporated.
Roughly chop the remaining four graham cracker sheets. Stir these along with the marshmallows and chocolate chips into the cookie dough. Scoop the cookie dough into 1-2" rounds and place on top of a graham cracker square. Refrigerate at least 30 minutes.
Bake for 12 minutes or until the edges turn golden brown. When they come out the oven, gently press a chocolate piece onto the tops of each cookie. Let cool 10 minutes.
