Preheat the oven: Set your oven to 325°F (165°C). Line a baking sheet with parchment paper or a silicone baking mat.
Combine the dry ingredients: In a large bowl, whisk together the sugar, cocoa powder, rice flour, tapioca flour, sorghum flour, chestnut flour, baking soda, salt, and xanthan gum.
Melt the chocolate: In the top of a double boiler over simmering water, melt butter with 4 ounces of chocolate chips and vanilla extract, stirring frequently to prevent scorching. Remove from heat once melted and smooth.
Mix the wet and dry: Stir the eggs into the dry ingredients, then gradually add the melted chocolate mixture. Mix until fully incorporated.
Fold in the chocolate chips: Gently fold 4 ounces of chocolate chips into the batter for those irresistible gooey pockets of chocolate.
Portion and bake: Drop tablespoon-sized balls of dough onto the prepared baking sheet, spacing them 2 inches apart. Bake for 12–15 minutes, or until the edges are set and the tops appear slightly cracked.
Cool the cookies: Allow them to cool on the baking sheet for 10 minutes, then transfer to a wire rack to cool completely. This step ensures the cookies maintain their chewy texture.