A quick, 2 ingredient buttermilk substitute, made with milk and lemon juice or vinegar. The recipe below the measurements needed to make a full cup of buttermilk, please see the graphic in the post for the ratios to use to scale down for different amounts of buttermilk
1Tablespoonlemon juice (fresh or bottled)may substitute 1 Tablespoon white distilled vinegar
1scant cup*milk
Instructions
Pour one Tablespoon of lemon juice (or one tablespoon of vinegar) into a liquid measuring cup.
1 Tablespoon lemon juice (fresh or bottled)
Add milk until liquid reaches the 1-cup line (at eye level).
1 scant cup* milk
Stir. The milk will thicken a little and may appear to be slightly curdled or chunky.
Use buttermilk in your recipe as instructed (note that this recipe yields a cup, please use only the amount called for in your recipe).
Video
Notes
*A scant cup just means just shy (usually 1-2 Tablespoons) of a full cup. In this instance, we're pouring the lemon juice into the measuring cup first, so, even though we're filling the milk up to the 1-cup line, the amount of actual milk that is used will be just less than a full cup, or a "scant cup".