Stir 1 tablespoon lemon juice or white vinegar into 1 cup milk to make a substitute for buttermilk. Alternatively, dissolve 1/2 tablespoon cream of tartar in 1 cup milk for similar results.
It is also possible to mix approximately 1/4 cup milk or water with 3/4 plain yogurt or sour cream to make a buttermilk substitute. Exact amounts may vary depending on the thickness of the yogurt or sour cream, but aim to achieve a consistency similar to that of buttermilk. Additionally, you may consider using plain kefir as a straight substitute for buttermilk. This is a convenient option as it does not require any other ingredients or preparation.