Milk + Lemon Juice or Vinegar (Best Option)
1 cup milk + 1 tablespoon lemon juice or white vinegar (let sit 5 minutes)This substitute works because the acid (lemon juice or vinegar) curdles the milk slightly, creating an acidic environment similar to buttermilk. The acidity is crucial for reacting with baking soda to produce carbon dioxide, which leavens the cake.
For best results, use whole or 2% milk and allow the mixture to sit for 5 minutes before adding to the batter. Avoid using skim milk as it reduces fat content and can affect texture.
The final cake will have a similar crumb structure, rise, and moistness as with buttermilk, making it the most reliable substitute in vanilla cake recipes.