Buttermilk isn't the most common ingredient to have stored in the fridge at all times. Luckily, if you forget to add it to your shopping list, there is a simple way to create buttermilk from scratch using what you have on hand. u003cbr/u003eu003cbr/u003eTo make 1 cup of buttermilk, you can either mix regular milk with white vinegar or lemon juice. For both vinegar and lemon juice, you just need 1 tablespoon of either and enough milk to measure 1 cup in total. Stir the ingredients and allow the mixture to sit for about 5 minutes.