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 eggs, melted butter, and vanilla extract, and whisk until smooth.
In a large bowl, combine cake mix with eggs and vegetable oil until smooth. Place the sprinkles into a shallow dish. Roll the cookie dough into balls, and roll each one into the sprinkles.
Evenly divide the brownie batter between the paper liners. Place one cookie dough ball over each brownie cup. Bake for 20-25 minutes.