Baking powder is a pre-mixed combination of an acid and a base; substitute by combining cream of tartar and baking soda to make homemade baking powder. These two ingredients form the majority of commercially produced baking powders.
Other acidic ingredients may be substituted if cream of tartar is not available. Replacing some of the baking liquid with an acidic liquid such as yogurt or buttermilk is a popular substitution. Single- and double-acting baking powder may be substituted for each other by changing the proportions in the recipe. Baking soda must be used in a baking powder substitution regardless of whether cream of tartar or another acid is used in the substitution.