Homemade Baking Powder (Corn Free)

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