How to Make an Easy Buttermilk Substitute
Need just a smidgen of buttermilk for a recipe, but don't want to bother buying a whole carton? The folks over at The Kitchn have got you covered. All you need is milk, and some lemon juice or white vinegar.
If we don't have buttermilk in the fridge, the closest substitute would be another dairy product with a little acidity added — milk with a spoonful of lemon juice or white vinegar does the job quite nicely. This mixture won't get as thick and creamy as buttermilk, but it will perform its role in the batter just as well. Incidentally, yogurt or sour cream thinned with milk (or plain water, in a pinch) also work well as buttermilk substitutes.