You can make a substitute for buttermilk by adding white vinegar or lemon juice to milk. Mix and let it sit for 5 to 10 minutes. To make 1 cup, use 1 cup of milk minus 1 tablespoon. Add 1 tablespoon of lemon juice. To make 2 cups, use 2 cups of milk minus 2 tablespoons. Add 2 tablespoons of lemon juice.