If you don't have 1/2 cup buttermilk on hand, try one of these easy substitutions. - 1/3 cup plain Greek yogurt + 3 Tablespoons water - 1/2 cup milk + 1 1/2 teaspoons lemon juice - 1/2 cup milk + 1 1/2 teaspoons white vinegar - 1/2 cup milk + 3/4 teaspoon cream of tartar - 1/3 cup sour cream + 3 Tablespoons water