Preheat the oven to the temperature indicated on the brownie mix box. Spray 2 8" round cake pans with nonstick cooking spray. Divide the batter between the prepared pans and bake according to the box instructions. Let cool on wire racks, then turn out of the pans. If the top of the cakes are domed, slice the tops with a serrated knife so you have an even, flat, cake. Put 1 brownie cake on a serving platter to form the bottom layer.
Fold the sour cream into the whipped cream. Spread the brownie with about half of the whipped cream mixture and half of the berries. Place the second brownie layer on top. Add a scoop of the whipped cream mixture and a few berries. Slice and serve with extra berries and whipped cream mixture.