As an adult, I have never purchased buttermilk. Buttermilk is simply soured milk. In an even more appetizing description, it is somewhat curdled and thickened as well. Buttermilk may not sound appetizing, but it is a fantastic thing when it comes to baking. The acid in the buttermilk reacts with baking soda in a recipe to create lighter and fluffier baked goods.
It is a simple matter to make your own buttermilk whenever it is called for in a recipe.
Acid + Milk + a few minutes to rest = Buttermilk
Add one tablespoon of lemon juice or white vinegar to a liquid measuring cup. Add milk until the amount reaches one cup. Let this mixture sit at room temperature for 5 minutes. The milk should look curdled. Stir the milk and use in any recipe that calls for buttermilk.
I've seen other methods using sour cream, plain yogurt and cream of tartar. I haven't tried them myself, but they should work just as well.
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