Whisk all ingredients in a bowl until fully blended.
Funnel into a clean, dry pint-size mason jar. Seal tightly.
Store in a cool, dry spot for up to 6 months (or longer if you add an oxygen absorber or refrigerate).
To Use as Buttermilk:
Mix ¼ cup of the dry mix with 1 cup water to equal 1 cup of liquid “buttermilk.”
