Pour milk into a glass measuring cup. Add distilled white vinegar OR lemon juice and allow to sit for about 10 minutes before use. The milk will thicken. Use as you would in a recipe that calls for buttermilk.
Recipe may be increased or decreased proportionately.
For dairy-free buttermilk, substitute your preferred non-dairy milk (coconut, soy, almond, rice, oat, etc) in place of the whole milk called for in the recipe.