Preheat oven to 350 degrees F. Line a baking sheet with parchment paper. Set aside.
In a medium bowl, whisk together flour, baking soda, salt, and cocoa. Set aside.
With mixer, cream butter and sugars together until smooth. Add in eggs and mix together well.
Gradually add flour mixture and beat until just combined. Stir in the chocolate chips and the marshmallows. Scoop the dough into rounded tablespoons or use any size cookie scoop and place on prepared baking sheet, about 2 inches apart.
Bake cookies for 8-12 minutes, depending on size and remove the baking sheet from the oven or until the cookies are set around the edges but still soft in the center.
Remove from oven. Press more marshmallows and chocolate chips gently into the tops of the cookies. Can top off with flaky sea salt or sprinkles if desired.
Let the cookies sit on the baking sheet for 5 minutes. Move to a cooling rack and cool completely.