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 a large bowl, mix together the cake mix, eggs, and vegetable oil until smooth. Fold in the sprinkles and M&Ms.
In a shallow dish, whisk together the granulated sugar and ground cinnamon. Roll the cookie dough into balls, and roll each one into the cinnamon sugar mixture. Place the cookies over each brownie cup. Bake for 20-25 minutes.
