1-Preheat the oven to 350F then line: Preheat the oven to 350F then line an 8×8 inch baking pan with parchment paper and set it aside.
2-Cream the butter, granulated sugar, and brown: Cream the butter, granulated sugar, and brown sugar until combined. Add in the egg and the vanilla extract and mix again.
3-Add in the flour, graham cracker crumbs,: Add in the flour, graham cracker crumbs, salt, baking soda, and mix just until the flour mixture disappears.
4-Press half of the dough evenly onto: Press half of the dough evenly onto the prepared baking sheet then remove that parchment from the pan and place in the freezer while you re-line the pan with more parchment paper and repeat the process with the leftover cookie dough.
5-Place the chocolate bars over the dough,: Place the chocolate bars over the dough, feel free to break pieces apart to fit the whole surface. Spread the marshmallow fluff or creme on top of the chocolate bar then gently flip the chilled cookie dough layer on top working carefully to keep it intact.
6-Bake the cookies in the preheated oven: Bake the cookies in the preheated oven for 25 minutes. Make sure you let the bars cool down fully before slicing into them to get that beautiful cross section that you see in my images.