Did you know that cornstarch is added to the baking powder you buy at the grocery store? It's added to powdered sugar too. The starch absorbs moisture and keeps the mixture from reacting before you need it in storage. The addition of cornstarch proved consternating as I am trying to eliminate corn from my diet, but then I found out that making your own baking powder is very easy. I don't know about powdered sugar yet - I'll tackle that one later.
Tapioca starch or potato starch can easily be substituted for cornstarch when making and storing your own baking powder. The ratio should be 2 parts cream of tartar, 1 part baking soda and 1 part starch flour. For example, to make 1/2 cup of baking powder:
1/4 cup cream of tartar
2 tbsp. baking soda
2 tbsp. tapioca starch
Sift together and store in an airtight container in a dry place.
If however you just need to use a small amount of baking powder immediately, the starch can be omitted. For example:
1 tsp. baking powder = 1/2 tsp. cream of tartar plus 1/4 tsp. baking soda
1 1/2 tsp. baking powder = 3/4 tsp. cream of tartar plus 3/8 tsp. baking soda
Don't let corn take you down. Now get baking!