Your ancestors collected buttermilk from the slightly sour liquid that was left after butter was churned. They used it in baked goods to add an airy texture. Buttermilk was also used as a woman's facial wash for a fresh complexion. Now, buttermilk is made from nonfat milk that has a culture called lactic acid added to it. Buttermilk has a thicker consistency than milk, with a yogurt-type flavor. Buttermilk is normally used to manufacture crème fraiche or as an enhancement to baked desserts, such as your cake mixes.
Preheat your oven to 350 degrees Fahrenheit. Spray your pans with nonstick cooking spray.
Put the cake mix into a mixing bowl. Substitute the amount of water called for in the cake mix directions with exactly the same amount of buttermilk, plus 1 or 2 tbsp. more, as buttermilk is slightly thicker than water. Add to your mixing bowl.
Add the amount of eggs and oil called for in the cake mix directions to the buttermilk and mix on medium speed with the mixer until it is well combined. Divide batter evenly between the cake pans.
Follow the box cake mix directions for baking. Remove the cake from the oven when it is done, and cool cake in the pans on the cooling rack.
Invert cake onto cooling rack according to cake mix instructions. Frost your cake when it is cooled.