Buttermilk

Whisk 1 part yogurt with 2 parts water (40 g yogurt plus 80 g water for 120 g buttermilk); a little thicker and more sour than true buttermilk, so loosen with extra water.

Same as yogurt: thin 1:2 with cold water and whisk until smooth; strain first if the dish needs a runny consistency.

Stir 15 g lemon juice into 250 g milk, leave 10 minutes, then stir; thinner and only lightly sour, so add a squeeze more lemon.