Preheat the oven to 350°F. Line an 8X8 pan with parchment paper.
Pulverize the graham crackers in a food processor or blender until a powder forms (very fine) set aside.
Using beaters or paddle attachment, cream the butter and dark brown sugar until fluffy, about 2 minutes.
Add the egg, egg yolk, and vanilla, mix until combined.
Whisk together the graham cracker powder, flour, cinnamon, salt, and baking powder.
Gradually add the dry ingredients while mixing on low. Mix until a dough forms.
Push ⅔rds of the cookie dough into the bottom of the pan, spreading it out evenly.
Spread the marshmallow fluff over the top, spreading it out evenly.
Sprinkle the chocolate chips evenly over the marshmallow.
Using the remaining ⅓rd of cookie dough, flatten small pieces spreading it out evenly on top of the chocolate chips (see photos in post)
Position it on the center rack of the oven to ensure even baking, avoiding placement too close to the top or bottom. Bake for 25 minutes or until the top is golden brown. Do not over bake, the bars will continue baking on the counter.
Enjoy when cooled down.