Preheat the oven to 350 F. In a large bowl, whisk together flour, sugar, cocoa powder, salt, and baking soda. Add in eggs, melted butter, and vanilla extract. Whisk until smooth.
In a medium bowl, whisk together flour, salt, baking soda, and cream of tartar. In a large bowl, combine butter with 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. In a small bowl, combine sugar and cinnamon. Pour the brownie batter into a greased square baking dish.
Evenly place the cookie dough over the brownie batter. Sprinkle the dough evenly with the cinnamon sugar mixture. Bake for 25-30 minutes.
