Step 1: In a large bowl, cream together the softened unsalted butter and brown sugar (or piloncillo) with an electric mixer until light and fluffy, about 2-3 minutes.
Step 2: Beat in the large egg and vanilla extract until well combined, scraping down the sides of the bowl as needed.
Step 3: In a separate medium bowl, whisk together the all-purpose flour, unsweetened cocoa powder, ground cinnamon, baking soda, salt, chili powder, and ground nutmeg.
Step 4: Gradually add the dry ingredients to the wet ingredients, mixing on low speed until just combined. Be careful not to overmix the dough.
Step 5: If using, fold in the semi-sweet chocolate chips by hand.
Step 6: Cover the cookie dough bowl with plastic wrap and refrigerate for at least 30 minutes to 1 hour. This helps prevent spreading.
Step 7: Preheat your oven to 350°F (175°C). Line baking sheets with parchment paper.
Step 8: Scoop rounded tablespoons of dough and roll them into balls. Place them about 2 inches apart on the prepared baking sheets.
Step 9: Bake for 10-12 minutes, or until the edges are set but the centers still look slightly soft. Do not overbake.
Step 10: Remove cookies from the oven and let them cool on the baking sheets for 5 minutes before transferring them to a wire rack to cool completely.