Preheat the oven to 350°F. Line baking sheets with parchment paper or use non-stick pans.
Measure the gluten-free flour, baking soda, and salt. Whisk to combine and set aside.
Melt the butter. Whisk the cocoa powder into the warm butter until dissolved. Let stand 2 minutes to bloom the cocoa powder.
Next, in a mixer bowl, cream the cocoa mixture together with the brown sugar on medium speed until well combined.
Add in the egg, egg yolk, and vanilla. Mix again to combine.
Blend in the dry ingredients.
Stir in the chocolate chips.
Roll 1 Tablespoon of dough into a ball, press a few extra chocolate chips into the outside of each ball if desired. (If the dough is too sticky to roll, just drop spoonfuls onto cookie sheets.)
Bake at 350°F for 8-9 minutes. Do not overbake the cookies. Let cookies set on the pan for 1-2 minutes before removing to a wire rack to finish cooling.
