At least four hours before baking the cookies, or ideally the night before: make the black cocoa cookie dough.

Set the butter in a microwave safe bowl and heat until mostly melted. Add the brown sugar and fine granulated sugar and whisk well. Return to the microwave and heat again, for 30 seconds. Whisk very well to combine, adding the salt and vanilla as you whisk.

Add the egg and whisk to combine. Add the dry ingredients: dutch process cocoa, black cocoa, flour, and baking soda and switch to a rubber spatula to stir until well mixed. Cover the bowl with plastic wrap to seal and set in the fridge for at least four hours, but ideally overnight (8-10 hours).

Take the cookie dough out of the fridge about 30-60 minutes before baking, so it’s easier to scoop and shape.

Preheat the oven to 350 F. Line two cookie sheets with parchment paper (a little grease helps it stick).

Use a disher to divide the cookie dough into portions that are about 1.5 tablespoons. Leave space between the dough balls as these will spread. Use your thumb or a rounded measuring spoon to make a small well (no bigger than a teaspoon) in the center of the dough. If you are using the caramel option, unwrap the candy and fold it to fit into the well. If using the peanut butter option, scrape a teaspoon of peanut butter into the well. Top the caramel or peanut butter with a teaspoon of marshmallow fluff. (Try to make sure the fluff is centered or it will melt off to the side).

Bake the cookies until the edges are set and cracked, they will look matte and have spread quite a bit - about 10 minutes. Let cool completely on the pan. Enjoy warm or at room temperature. Store leftovers in an airtight container.