Make the dough the night before baking, or at least 4 hours before. It needs a long chill.

Grind the graham crackers in a food processor until you have fine crumbs (60g or ½ cup).

Set the butter in a large heatproof bowl (113g or ½ cup). Set it in the microwave to melt (alternatively melt the butter in a saucepan then transfer to the bowl).

Add the salt, vanilla, brown sugar (67g or ⅓ cup), fine granulated sugar (100g or ½ cup) to the bowl and whisk very well. Return the bowl to the microwave and heat for another 30 seconds.

Whisk very well, for about 30 seconds. The mix will turn shiny and begin to become more cohesive. Add the egg and whisk very well, until shiny.

Measure in the peanut butter (135g or ½ cup) and whisk to combine. Add the baking powder (½ tsp), baking soda (½ tsp), and flour (170g or 1 ¼ cups), and graham cracker crumbs and stir with a rubber spatula until fully combined and no streaks of flour remain.

Cover the bowl to seal with plastic wrap and set in the fridge overnight, or for at least 4 hours.

When ready to bake, preheat the oven to 350 F. Grease then line two cookie sheets with parchment paper.

Use a cookie disher to scoop out dough balls that are 1 ½ tablespoons per cookie. Leave enough space for them to spread; at least an inch diameter. Use the bottom of a tablespoon or your thumb to indent the middle of the dough ball to make a little well in the center (this is where you’ll put the filling).

Add about a heaped teaspoon of marshmallow fluff to the center of the cookie, into the well. On top, place a peanut butter cup. Do your best to center everything or the toppings will slide off in the oven.

Bake the cookies until they’ve spread, the chocolate is fully melted and the edges are turning golden brown, about 10 minutes. IF you like, sprinkle more graham cracker crumbs on top of the melted chocolate. Let cool on the pan; while hot the cookies are soft but will firm up as they cool.