Mix Dry Ingredients: In a medium bowl, whisk together the flour, cocoa powder, baking soda, salt, cinnamon, and chili powder. Set aside.
Mix Wet Ingredients: In a large bowl with a hand or stand mixer, beat the butter and both white and brown sugar together on medium-high speed until light and creamy, about 2 minutes. Add the egg and vanilla, and beat until smooth.
Combine Wet & Dry Ingredients: Reduce mixer speed to low. Add the dry ingredients in two additions, mixing until no dry streaks remain.
Add Chocolate Chunks: Stir in the chocolate chunks by hand.
Chill the Dough: Cover the bowl with plastic wrap and refrigerate for at least 1 hour (or up to overnight). Chilling ensures the cookies stay chewy and don’t spread too much.
Prepare Coating: In a small bowl, combine the granulated sugar and cinnamon
Shape & Roll: Preheat the oven to 350°F (175°C). Line two baking sheets with parchment paper. Scoop the dough into 2-tablespoon portions (about 1 ounce each), roll into balls, and coat each in the sugar mixture. Place 3 inches apart on the prepared baking sheets.
Bake: Bake for 10–12 minutes, until edges are set but centers look slightly soft. Let cookies cool on the baking sheet for 5 minutes before transferring to a wire rack.