To use cake mix in a brownie recipe, make the cake mix using fewer eggs and a smaller amount of liquid than is specified in the mix instructions. The cake mix takes the place of flour, cocoa and sugar. The exact measurements vary by recipe.
Cooks.com offers an extremely simple recipe for cake mix brownies. To make this recipe, combine 1 box of chocolate cake mix, 1/4 cup of cooking oil, 1/3 cup of water and 1 egg. Mix the ingredients well, then pour into a greased or lined 9- by 13-inch pan, and bake at 350 degrees Fahrenheit until a toothpick inserted into the center of the brownies comes out clean.
Cookies and Cups' recipe for cake mix brownies uses Pillsbury Moist Supreme Dark Chocolate cake mix. This cake mix normally calls for 1 1/2 cups of water, 1/3 cup of oil and 3 eggs. In the brownie recipe, 1 box of the cake mix is combined with 1/4 cup of vegetable oil, 1/3 cup of milk and 1 egg. This recipe also calls for 10 ounces of chocolate chunks for extra fudgy brownies. Mix all the ingredients, and pour into a greased 8- by 8-inch baking pan. Bake at 350 degrees Fahrenheit for about 20 minutes.