Preheat the oven to 350 degrees. Spray 2 - 8” cake pans with nonstick cooking spray containing flour. (May also cut parchment paper circles for the bottom of each pan to prevent sticking)
In a large bowl, whisk together the brownie mix, sugar, flour, baking powder, cocoa powder and salt. Add in the wet ingredients: melted butter, sour cream, water, vanilla and eggs and whisk until well combined. Stir in the mini chocolate chips.
Divide the cake batter equally between the two cake pans and place in the oven and bake for 30-35 minutes, or until a skewer/knife comes out cleanly. Let the cake cool in the pans for about 10 minutes before removing and placing on a cooling rack to come to room temperature.
Make the frosting or use 1 tub of ready made. Place the first layer of cake onto a serving platter or cake pedestal and scoop about ½ c of frosting and spread it in an even layer over the cake. Place the second layer of cake and use a spatula to create a thin layer of frosting all over