Preheat the oven to 350 F. In a medium bowl, whisk together flour, cocoa powder, salt, baking soda, and cream of tartar. In a large bowl, combine butter with granulated sugar and brown sugar until fluffy.
Add in egg and vanilla extract, and mix until smooth. Add in the flour mixture and mix until it is fully combined. Add in the red food coloring and mix until it is fully red.
In a small bowl, combine granulated sugar and ground cinnamon. Press the cookie dough into a greased 8-inch square baking dish. Sprinkle with the cinnamon sugar mixture. Bake for 20-25 minutes.