In a medium-size, microwave-safe bowl, place the chopped chocolate and chopped butter.
Melt in a double boiler or in the microwave in 30-second bursts at 50% power, stirring until smooth. Allow the mixture to cool briefly.
To the melted butter and chocolate, add the molasses, brown sugar, and egg. Mix to combine, and set the bowl aside.
In a large mixing bowl, place the flour, xanthan gum, cocoa powder, salt, and baking soda, and whisk to combine well.
Create a well in the center of the dry ingredients, and add the chocolate mixture. Mix to combine. The dough will be very soft.
Transfer the dough to a large piece of unbleached parchment paper. Shape the dough into a cylinder about 2-inches in diameter and about 8-inches long along the length of the parchment paper.
Roll the paper tightly, cinching the ends to seal.
Place the cylinder of dough in the refrigerator until firm enough to slice (at least 1 hour).
Once the dough has chilled enough to be sliced, preheat your oven to 325°F. Line large rimmed baking sheets with unbleached parchment paper and set them aside.
Remove the chilled cylinder of dough from the refrigerator and unwrap it. Rock the cylinder back and forth on a flat surface to round out any flattened edges.
Using a large, sharp knife, attempt to slice the cylinder at the very end. If it's too difficult to slice without splintering the dough, let it sit until it's sliceable but still firm.
Slice into 1/2-inch thick disks by cross-section. You should get about 16 cookies.
Cup each slice separately in your palm to reshape any rounds that have become misshapen during slicing.
Place the (optional) granulated sugar in a small bowl. Dip each of the raw cookie disks in the sugar, pressing gently to coat on all sides.
Place the disks of dough about 2 inches apart on the prepared baking sheets. They will spread during baking.
Place the baking sheets, one at a time, in the center of the preheated oven for 12 minutes, or until the cookies are spread about 3 inches in diameter and don't seem shiny wet in the center.
Allow to cool completely on the baking sheet before serving. If you attempt to move the cookies before they are cool, they will fall apart but will be stable once set.
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Notes
Flour blend notesThis recipe works best with Better Batter’s original all purpose gluten free flour blend, Nicole’s Best multipurpose with added xanthan gum, or Bob’s Red Mill 1-to-1 in the blue bag. If you aren't chilling the raw dough overnight before baking, add an extra ½ teaspoon xanthan gum to Nicole's Best or an extra 1/4 teaspoon xanthan gum to Bob's.To make your own high-quality gluten free flour blend, check out my mock all purpose gluten free flour blends.