DIY Buttermilk Recipe! For when you need buttermilk, but you forgot to buy it. The best substitute for buttermilk is milk with a bit of lemon or white vinegar to add a little acidity, even though it won't be as thick or creamy as buttermilk. Yogurt or sour cream thinned with milk is a great substitute as well! Makes 1 cup. Ingredients 1 cup milk (whole, 2%, or heavy cream) 1 tablespoon lemon juice or white vinegar 1. Measure 1 scant cup of milk. Stir in 1 tablespoon of lemon juice or white vinegar. 2. Let stand for 5-10 mins at room temperature. Milk will thicken slightly and you will see some curdled bits. 3. Use it just as you would buttermilk! Other Buttermilk Substitutes: Yogurt: Mix 3/4 cup plain yogurt with 1/4 cup water to thin. Sour Cream: Mix 3/4 cup sour cream with 1/4 cup plain water to thin. Cream of Tartar: Mix 1 cup of milk with 1 3/4 teaspoons cream of tarter. Let stand 5-10 minutes until slightly thickened and curdled.