Preheat oven to 350°F (176°C). Grease or line a baking sheet with parchment paper.
In a medium bowl, whisk together the flour, cocoa powder, baking soda and salt.
In a large bowl, cream together the butter and sugar until light and fluffy. Add in the eggs and vanilla extract and mix until combined.
Gradually add in the dry ingredients and mix until just combined. Fold in the marshmallows and chocolate chips.
Form cookie dough into 1-inch balls and place on prepared baking sheet. Bake for 8-10 minutes or until edges are set. Allow to cool on baking sheet for 5 minutes before transferring to a wire rack to cool completely.
Interesting Facts
These cookies are best eaten fresh, but can be stored in an airtight container for up to 5 days.
You can add different kinds of chips, such as peanut butter, white chocolate, or butterscotch chips.