Chocolate Dough

1. Preheat oven to 350°F. Butter (grease) and line a 9×9 baking dish with parchment paper.
2. In a small mixing bowl, whisk together flour, cocoa powder, baking soda, cornstarch and salt. Set aside for later.
3. In a stand mixer bowl or hand mixer, cream butter and dark brown sugar until combined.
4. Add the egg and vanilla to the butter mixture. Mix until just combined.
5. Mix in the flour mixture to the wet ingredients. Transfer the dough to plastic wrap and place in the refrigerator to chill while you make the peanut butter dough.

Peanut Butter Dough

1. In a small mixing bowl, whisk together flour, baking soda, salt and cornstarch. Set aside for later.
2. In a stand or hand mixer, cream together butter and peanut butter. Mix until combined. Add in sugar and light brown sugar. Mix until combined.
3. Add egg and vanilla to the butter mixer and mix until just combined.
4. Mix in the flour mixture into the wet ingredients. Once the dough has just mixed together, it’s time to marble the dough.

Marble the Dough

1. To make this process easier, divide the dough into quarters. This will help you to work with the dough a bit easier as your marble it.
2. With one quarter peanut butter dough and one quarter chocolate dough, smush the two together, flatten the dough, pull the dough, place one dough piece back on top of the other and roll it into a ball. Repeat this for the remaining three dough balls.

Assemble and Bake

1. Add half the cookie dough (2 marbled balls) to the prepared baking dish. Press the dough in an even layer to the bottom of the pan.
2. Spread marshmallow fluff across the top. *Tip: Lightly grease a spatula to spread the fluff. This won’t make it stick to the spatula.
3. Add dollops of the remaining dough to the top of the marshmallow fluff. Gently press Nutter Butter cookies, Hershey chocolate pieces and graham cracker pieces on top.
4. Bake for 25-30 minutes, until the top is lightly browned. You may need some extra time depending on how your oven bakes, so start with 2-3 minute additional intervals at a time. Once baked, remove from oven and transfer to a cooling rack. Let the cookie cool completely and then cut into bars.
5. Enjoy with for a treat after dinner with a cup of coffee or tea.