Place the chopped chocolate and chopped butter in the microwave and melt till smooth.
Remove from the heat and add the molasses, vanilla and sugar, mix to combine and set aside to cool briefly.
Combine the flour, xanthan gum, cocoa powder, salt and baking soda.
Create a well in the center of the dry ingredients, and add the chocolate mixture.
Mix to combine. Add the egg, and mix to combine again.
Divide the dough into two portions and transfer each to a large piece of parchment paper.
Shape each piece into a cylinder about 1 ½ inches in diameter along the length of the parchment paper and roll the paper tightly, twisting the ends to seal.
Place the two cylinders of dough in the refrigerator for 1 hour.
Preheat your oven to 325°F.
Line large baking sheets with parchment paper and set them aside.
Remove the chilled cylinders of dough from the refrigerator, unwrap, and slice into 1 inch thick disks.
Place the pieces of dough about 3 inches apart on baking sheets.
Bake until the centre is set.
Remove from the oven and allow to cool on sheet for several minutes before moving to a wire rack to cool completely.