Preheat the oven to 350 F. In a large bowl, whisk together flour, sugar, cocoa powder, salt, and baking soda. Add in melted butter, eggs, and vanilla extract and whisk until smooth.
In a medium bowl, whisk together flour, salt, and baking soda. In a large bowl, combine butter with peanut butter, granulated sugar, and brown sugar until fluffy.
Add in egg and vanilla extract, and mix until smooth. Add in the flour mixture, mix until it is fully combined.
Pour the brownie batter into a greased 8-inch square baking dish. Evenly press the cookie dough over the brownie batter. Bake for 25-30 minutes.
