Stir brownie mix, 2 eggs, ½ cup canola oil, and ¼ cup water in a bowl. Just as with any brownie recipe, only stir until fully incorporated. I wouldn't use an electric mixer for the brownie batter. Set aside
With a mixer, mix 2 tablespoons canola oil, 1⅓ cup water, 3 egg whites and cake mix in a large bowl on low speed until combined. Then mix on medium speed for 2 minutes.
Pour brownie batter into a greased 9x13 baking dish. Carefully pour cake batter over the brownie batter. (I almost wonder if it would work to swirl the two with a knife!)
Bake in the preheated oven until golden and the tops spring back when lightly pressed - about 20 minutes. You will know it is finished if a toothpick inserted comes out clean. I personally don't mind the brownie batter being a little underdone.
Top with your favorite frosting and garnish if desired.
Recipe by Clever Housewife at http://cleverhousewife.com/2012/01/brownie-cake-recipe-heaven/