Preheat oven to 350 F and line baking sheets with parchment paper.
In a large bowl or stand mixer cream together butter and sugars until light and fluffy.
Add in vanilla, egg, and egg yolk. Beat until mixture is well combined.
In a second bowl whisk together flour, baking soda, baking powder, and salt.
Add dry ingredients into wet and mix until combined.
Fold in the chocolate chips and graham cracker pieces.
Using a medium cookie/ice cream scoop3 tbsp worth of dough, push your knuckle in the centre to create a whole. Add half a marshmallow pieces inside and gently squeeze the sides to secure the marshmallow. The marshmallow should be visible in the centre to the cookie dough ball.
Place the balls on to the baking sheet 2 inches of space between cookies.
Bake for 10-12 minutes or until cookies are golden brown on the edges. Top warm cookies with extra chocolate and graham cracker pieces.
Let the cookies cool to room temperature on the baking sheet before moving.
