Preheat your oven to 350°F (175°C). Line a baking sheet with parchment paper or a silicone baking mat.
In a medium bowl, sift together the all-purpose flour, cocoa powder, baking soda, salt, ground cinnamon, and cayenne pepper. Whisk to combine and set aside.
In a large bowl, use an electric mixer or hand whisk to cream the softened unsalted butter and granulated sugar until light and fluffy, about 2-3 minutes.
Beat in the large egg and vanilla extract until fully incorporated.
Gradually add the dry ingredients to the wet mixture, stirring gently with a spatula or mixer on low speed. Mix just until combined.
Fold in the dark chocolate chips evenly throughout the dough.
Use a tablespoon or cookie scoop to drop rounded dough balls onto the prepared baking sheet, spacing about 2 inches apart. Bake for 10-12 minutes, until edges are set but centers remain slightly soft.
Allow cookies to cool on the baking sheet for 5 minutes before transferring to a cooling rack to cool completely.