Boxed brownie mixes advertise their convenience compared to homemade brownies—with only a few ingredients, they promise a moist, chocolatey crumb. However, these "instant" mixes still require fresh ingredients and a baking time that matches that of homemade brownies. When you're craving a chocolate fix but you're coming up short on eggs, oil, and time, don't despair: you can still make brownies using a can of soda.