Whisk together the gluten free flour blend, cocoa powder, baking soda, and fine sea salt together in a small bowl. Set aside.

Add the softened butter and brown sugar to the bowl of a stand mixer fitted with the paddle attachment. Beat on medium speed until light and fluffy-- about 2 minutes.

Next add the egg and vanilla and mix to combine. Make sure to scrape down the sides of the bowl as needed.

Add the dry ingredients and mix on low just until the dry ingredients are fully combined.

Scoop 1 tablespoon-sized balls onto the parchment-lined baking sheet, I used an OXO Small Scoop. Refrigerate for at least 30 minutes or overnight (cover with plastic wrap if refrigerating overnight).

Preheat your oven to 350F and line two large baking sheets with parchment paper or silicone baking mats.

Roll each ball of cookie dough in granulated sugar and place the cookie dough balls on the baking sheet, making sure to place them at least 2” apart.

Bake the cookies in batches (about 8-12 cookies per sheet) for 8-10 minutes, or until the edges are set but the center is still soft.

When the cookies come out of the oven, Immediately place a Hershey's Kiss into the center -- press down only slightly. The chocolate will melt and glue the kiss to the cookie.

Let the cookies cool on the tray for 5 minutes then transfer the cookies to a wire rack to cool.

Sprinkle with sea salt before serving, if desired.

Store any leftover cookies in an airtight container at room temperature for up to three days.