Weigh out the ingredients
You'll need flour, cocoa powder, sugar, baking powder, baking soda, salt, butter, egg, vanilla, and marshmallows.
Combine dry ingredients
In a medium bowl, combine the flour, black cocoa powder, baking powder, baking soda, and salt.
In the bowl of a stand mixer fitted with a paddle attachment, cream together the butter and sugar until light & fluffy for 2-3 minutes.
Cream butter & sugars
Mix in the egg and vanilla until fully combined.
Mix in egg & vanilla
Scrape down the bowl with a rubber spatula, then mix in the dry ingredients on low speed until fully combined. The dough will be very thick.
Mix in dry ingredients
Use a 1 tablespoon cookie scoop to portion the cookie dough. Flatten out one cookie dough ball just enough to fit one marshmallow half. Flatten out a second cookie dough ball very thin and rip a small hole in the center, then place on top of the marshmallow.
Shape the cookie dough
Gently roll into a ball and barely seal the hole, then roll in sugar. The sealed hole will ensure the marshmallow peaks through in the center.
Roll cookie dough in sugar
Place the stuffed cookie dough balls on the prepared baking sheets spaced about 3 inches apart. Bake the cookies for 12 minutes until cracked and the marshmallows peak through.
Remove from the oven, and immediately use a large round cookie cutter or glass to scoot the edges in to create perfectly round cookies. Allow to completely on the baking sheet and enjoy!