If you'll be needing to keep them warm, you can preheat oven to 250° F (otherwise ignore).
Whisk the flour, cocoa powder, cornstarch, sugar, baking powder, baking soda, and salt in a large bowl (and the cinnamon or espresso if you're using it).
Make a well in the center and add the eggs, buttermilk, melted (slightly cooled) butter or oil, and vanilla.
Stir together until everything is *just* incorporated, but then stop (you don't want to overmix). Fold in the chocolate.
Heat your waffle iron until very hot. Mine doesn't need non-stick spray, but make sure whether yours does or not.
One at a time, cook the waffles until done and crispy. Transfer to a wire rack and keep warm in oven until ready to serve (you can also reheat in a toaster oven). Serve with peanut butter and maple syrup.