Preheat oven: Set to 350°F (175°C) and line a baking sheet with parchment paper.
Mix wet ingredients: In a large bowl, cream together butter, granulated sugar, and brown sugar until smooth. Add pumpkin puree, egg, and vanilla; mix until combined.
Combine dry ingredients: In a separate bowl, whisk together flour, cocoa powder, baking soda, salt, and cinnamon.
Form the dough: Gradually add the dry ingredients to the wet mixture, mixing until just combined. Fold in chocolate chips.
Scoop cookies: Drop spoonfuls of dough onto the prepared baking sheet, spacing about 2 inches apart.
Bake: 12–15 minutes, until cookies are set but still soft in the center.
Cool: Let cookies cool on the baking sheet for 5 minutes, then transfer to a wire rack to cool completely.
