Use it to clabber milk - here's how to make a buttermilk substitute using cream of tartar:
Combine 1 cup milk, 1 Tbl lemon juice or distilled vinegar and 1/2 tsp Cream of Tartar. Let the mixture sit for about 5 minutes to allow the milk to curdle. Stir to combine and use as you would buttermilk. This homemade buttermilk substitute works well in pancake batter and biscuit dough. It provides acidity and tanginess similar to traditional buttermilk, helping to tenderize baked goods and add flavor.