Preheat your oven to 350°F (175°C) and line a baking sheet with parchment paper.

In a bowl, whisk together the flour, cocoa powder, baking soda, and salt. Set aside.

In a large bowl, beat the softened butter and sugar together until fluffy, about 2-3 minutes.

Mix in the egg and vanilla extract until well combined.

Gradually add the dry ingredient mixture to the wet ingredients, mixing until just a few swirls of flour remain.

Gently fold in the chocolate chips until evenly distributed.

Using a cookie scoop, take a generous amount of dough, flatten it slightly, and place 1 or 2 mini marshmallows in the center.

Seal the dough back around the marshmallow and place the filled cookies on the prepared baking sheet about 2 inches apart.

Bake for 10-12 minutes until the edges feel set but the centers remain soft.

Allow the cookies to cool on the baking sheet for 5 minutes before transferring them to a wire rack to cool completely.