Preheat the oven to 350ºF (180ºC). Line two baking pans with silicone baking mats or parchment.

In a medium bowl, combine the flour, cocoa powder, xanthan gum/psyllium husk powder (if using), baking powder, baking soda, and salt, and whisk thoroughly. Set aside.

In the bowl of a stand mixer fitted with the paddle attachment, combine the butter and two sugars. Mix on medium speed until light and fluffy.

Add the eggs, one at a time, mixing on medium and scraping down the bowl between additions. Mix in the vanilla.

Add the flour mixture in three to four additions, mixing on low speed until just combined, and scraping down the bowl as needed.

Add the chocolate chips, and mix on low just until they are evenly distributed. (At this point, the dough may be refrigerated for up to two days, baking off when needed. Alternately, you can freeze the dough, scooped into balls, for up to three months. Thaw overnight before baking.)

Scoop the cookie dough onto your prepared baking pans. Depending on the size cookie you decide to make, you should be able to fit anywhere from five to 12 cookies on each pan. Lightly press down on the balls with the palm of your hand to flatten them, and sprinkle the surface with kosher salt.

Cookies are phenomenal warm, but will still taste incredible at room temperature. They keep, wrapped airtight at room temperature, for up to three days.