Heat oven to 350 degrees F. Line 22 muffin cups with white paper liners.
Follow the box instructions, putting all the ingredients in a large bowl, using the buttermilk in place of the water specified on the package, 1/3 cup oil and 4 eggs (instead of 3). Beat with an electric mixer until moistened, about 30 seconds. Increase the speed to high and beat until thick, 2 minutes longer.
Spoon about half the batter into a resealable plastic bag. Snip a 1/4-inch corner from the bag and fill paper liners two-thirds full. Repeat with remaining batter. Bake 15 to 18 minutes, until golden and a toothpick inserted in the center comes out clean. Remove cupcakes from pan to a rack and allow
to cool completely before decorating.