Whisk flour, cocoa powder, baking soda, salt, cinnamon, chili powder, and cayenne together.
Beat butter, granulated sugar, and brown sugar until smooth and fluffy.
Add egg and vanilla extract and mix until combined.
Add dry ingredients and mix just until a soft dough forms. Fold in chocolate chunks if using.
Cover and refrigerate dough for 30 minutes.
Preheat oven to 350°F (175°C) and line baking sheets.
Mix rolling sugar and cinnamon in a small bowl.
Scoop tablespoon-sized dough portions, roll into balls, then coat in cinnamon sugar.
Place cookies 2 inches apart on baking sheets.
Bake 10–12 minutes until edges are set and centers are soft.
Add mini marshmallows during the last 2 minutes if using.
Cool on baking sheet for 5 minutes, then transfer to a rack.
Notes
• Spice should be warming, not overpowering
• Chilling prevents excess spreading
• Do not overbake for soft centers
• Cinnamon sugar coating enhances aroma and texture