Preheat your oven to 350°F (175°C) and line a baking sheet with parchment paper. In a medium bowl, whisk together the flour, cocoa powder, baking soda, and salt. Set aside.

In a separate large bowl, cream the softened butter, granulated sugar, and brown sugar together until light and fluffy. Add the egg and vanilla extract and beat until combined. Gradually add the dry ingredients to the wet ingredients, mixing just until incorporated. If the dough feels a bit too dry, add a tablespoon or two of milk to achieve a soft, doughy consistency.

Fold in the mini chocolate chips, ensuring they’re evenly distributed throughout the dough.

Scoop tablespoon-sized portions of dough and roll them into balls. Place them on the prepared baking sheet, leaving about 2 inches between each cookie. Gently flatten each dough ball with your fingers or the bottom of a glass.

Bake the cookies in the preheated oven for 8–10 minutes, or until the edges are set but the centers are still soft. Remove from the oven and immediately press a few mini marshmallows into the center of each cookie. Return the cookies to the oven for an additional 1–2 minutes, allowing the marshmallows to melt slightly.

Let the cookies cool on the baking sheet for a few minutes before transferring them to a wire rack to cool completely