Preheat the oven to 350 F. Line a 12 cup muffin pan with paper liners. In a large bowl, whisk together flour, sugar, cocoa powder, salt, and baking soda. Add in the eggs, melted butter, and vanilla extract until smooth.
Evenly divide the brownie batter between the prepared muffin pan. In another large bowl, mix together cake mix, eggs, and vegetable oil until smooth. Fold in the sprinkles. In a shallow dish, mix together granulated sugar and ground cinnamon.
Roll the cookie dough into balls, and roll each one into the cinnamon sugar mixture. Place over each brownie batter. Bake for 20-25 minutes.
