Preheat the oven to 375F. Line two baking sheets with parchment paper.

In a medium bowl, whisk together the flour, cocoa mix, salt, baking powder, and baking soda.

In a large bowl or the bowl of a stand mixer with the paddle attachment, beat the butter and sugars together on medium speed until light and fluffy, about 3 minutes. Add the egg and vanilla and beat until well combined, stopping to scrape down the bowl. Add the flour mixture and mix on low speed just until combined. Mix in the chocolate chips.

Scoop the dough into balls using a 1 ½ tablespoon spring-loaded scoop, and place on the baking sheets 2 inches apart.

Bake 1 sheet at a time for 9 minutes. Remove the cookies from the oven, and place a marshmallow half, cut side down, or 3 mini marshmallows in the center of each cookie. Return to the oven and continue baking for 2 minutes. Cool for a few minutes on the baking sheet and then transfer to a wire rack to cool completely.