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.
In another large bowl, mix together cake mix with eggs, vegetable oil and peanut butter until smooth. Evenly divide the brownie batter between the prepared muffin pan. Top with the cookie dough. Bake for 20-25 minutes.