Milk + Lemon Juice or Vinegar (Best Option)
1 cup milk + 1 tablespoon lemon juice or white vinegar (let sit 5-10 minutes)This substitute works because the acid (lemon juice or vinegar) curdles the milk slightly, mimicking the acidity and texture of buttermilk. The acid reacts with baking soda in the cupcake batter to produce carbon dioxide, which helps the cupcakes rise and creates a tender crumb.
For best results, use whole or 2% milk and allow the acid to sit in the milk for at least 5 minutes before adding to the batter. This ensures proper curdling and acidity. Avoid using skim milk as it may reduce richness.
Compared to original buttermilk, this substitute yields very similar texture and flavor, with only a slight difference in tanginess that is generally imperceptible in cupcakes.