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

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

In a large bowl, cream together the softened butter, granulated sugar, and brown sugar until light and fluffy, about 3-4 minutes.

Beat in the eggs one at a time, then stir in the vanilla extract.

Gradually add the dry ingredients to the wet mixture, mixing until just combined.

Fold in the chocolate chips and mini marshmallows until evenly distributed.

Drop rounded tablespoons of dough onto the prepared baking sheets, spacing them about 2 inches apart.

Bake in the preheated oven for 10-12 minutes, or until the edges are set but the centers are still soft.

Remove from the oven and let the cookies cool on the baking sheets for 5 minutes before transferring them to wire racks to cool completely.