First, preheat oven to 350 degrees Fahrenheit. Line a baking pan with parchment paper.
In a stand mixer, beat butter, brown sugar and granulated sugar for 1 minute or until no clumps of butter remain.
Add in vanilla extract and egg. Mix to combine.
Add in gluten free flour, cocoa powder and baking soda. Stir until a thick and sticky dough forms.
Fold in chocolate chunks and mini marshmallows.
Spray a cookie scoop or ice cream scoop with nonstick spray. Then scoop balls of dough onto lined baking pan. Keep at least 2 inches between each ball of dough since these cookies spread a lot.
Bake for 9 to 10 minutes or until cookies are set in the middle.
Finally, remove from oven. Allow cookies to cool on pan for 10 minutes before transferring to a cooling rack.
