Preheat your oven to 350°F. Line a baking sheet with Silpat or parchment paper and set aside.
In a stand mixer fitted with the paddle attachment, cream the butter and sugars together until the mixture becomes light and airy, about 2 minutes. Scrape down the bowl and add the egg and vanilla, beating until well combined.
In another bowl, sift together the flour, cacao powder, espresso powder, baking soda, and salt.
Next, add the dry ingredients into the butter mixture, stirring until just combined.
Gently fold in the chocolate chips, being careful not to over mix the dough.
Spoon about 1/4 cup of the fluff into the batter and fold once or twice. Your fluff will get marbled and incorporate into the dough when you scoop the cookies out, so you want to make sure not to over mix.
Use a large cookie scoop to portion out ~1-inch cookie-dough spheres on the prepared cookie sheet about 2 inches apart. Try to scoop the dough so as to evenly distribute the fluff. As you portion the dough, you can spoon and swirl more marshmallow fluff over the cookie to make sure each cookie has a good amount of fluff without over incorporating.
Bake for 5 minutes, then remove from the oven and sprinkle with graham cracker crumbs to taste. Return to the oven, and bake for 5-6 minutes, until the edges are firm but the center is still soft.
Let cool on a rack for 10 minutes before serving, then enjoy.