Using an electric mixer, beat together the softened butter, sugars, egg, egg yolk, and vanilla extract. Beat until combined and be sure to scrape the side of the bowl.
Add flour, baking soda, baking powder, salt and mix until combined. Add in the graham cracker crumbs, mini marshmallows, and mini chocolate chips. Mix together until all of the ingredients are incorporated.
Place the cookie dough in the refrigerator to set for 30 minutes.
Preheat oven to 375 degrees F. Line cookie sheets with a silpat mat or parchment paper. Using a medium cookie scoop or scoop 2 tablespoons of cookie dough on the baking sheet about 3 inches apart (there will be 9 cookies on each baking sheet).
Gently press pieces of the chocolate bar and graham crackers on top of each cookie. Bake for 7-9 minutes and then remove from the oven and add 2-3 mini marshmallows to each cookie. Bake for another 3 minutes until the marshmallows are melted and the cookies are golden brown.
Let the cookies cool for a few minutes and enjoy!