In a medium mixing bowl combine flour, cocoa powder, cinnamon, salt, baking soda, cornstarch, espresso powder and a pinch of cayenne (optional). Set aside.
In the bowl of a stand mixer (or mixing bowl with hand mixer) cream together butter, ½ cup brown sugar and ½ cup granulated sugar for 2-3 minutes until well combined and fluffy.
Add in egg and vanilla extract and beat for additional minute or 2 until well combined.
Add in half of the dry mixture to the butter mixture and beat low for around 20 seconds until combined. Then repeat with the remaining dry mixture and beat on low until combined.
Add in 1 cup of chocolate chips and 1 cup of marshmallows and beat on low for 5-10 seconds until just combined. (do not over mix)
Cover the dough with cling wrap and chill in the refrigerator for at least 1 hour (ideally 2) and up to 2 days.
After chilling, take the dough out of the fridge and let it sit on the counter for about 10 minutes. Preheat the oven to 350 degrees F. Line cookie sheets with parchment paper.
In a shallow bowl or plate, mix together ⅓rd cup of granulated sugar and ½ tsp of cinnamon.
Use a cookie scoop, measure out about 2 tbsp of dough use your hands to roll into a ball. Roll the ball in the cinnamon sugar mixture until the outside is coated.
Place the coated cookie dough balls on the parchment lines cookie sheets about 2-3 inches apart. *Note* if there are large marshmallows visible in the dough try to place the cookie so that they are facing up. If they are on the bottom they can make the cookies spread a bit more. Still very tasty and gooey, but not as visually pleasing. Repeat the process until the dough has been used up. You should get between 24 and 28 cookies.
Bake the cookies at 350 degrees F for 9-10 minutes. Remove from the oven and let cool on the cookie sheet for about 5 minutes then move to a wire rack to cool. Enjoy!