The two of them combined work like double-acting baking powder. When substituting for cream of tartar, you must also substitute for the baking soda at the same time. If there is additional baking soda that does not fit into the equation, simply add it to the batter. When cream of tartar is used in whipping egg whites, it acts as a stabilizer. There is no exact substitute, but you can add a pinch of salt instead.
Salt has a lesser stabilizing effect.
Q. I noticed some of the recipes call for sour milk. To make your own sour milk, add a tablespoon of vinegar or lemon juice to a cup measure and fill the remainder of the cup with fresh milk. Let the mixture stand for 5 minutes before using it in a recipe. Q. I often find myself adjusting recipes in order to make enough for my family, but it doesn't quite work for some recipes. You may want to see our Measurement Conversions page for answers to any of your measurement-related questions.