Preheat oven to 350 degrees F. Line a baking sheet with parchment paper.
Place roasted chestnuts in a food processor, and grind until crumbly and fine.
In a large bowl, combine ground chestnuts, coconut flour, coconut sugar, and baking soda.
In a separate bowl, whisk together coconut oil, egg, and vanilla extract. Pour this mixture into the dry ingredients and mix well.
Fold in chopped chocolate.
Scoop with a large rounded tablespoon to drop dough onto the lined baking sheet. Flatten slightly.
Bake for 10-12 minutes, until slightly golden brown.
Cool completely before serving.