Baking Powder

One of my SILs brought to my attention that I have not posted how I make baking powder. I cannot buy it in the store, because the ones I have found have corn starch in them. 1/2 tbsp. cream of tarter 1/4 tsp. baking soda 1/4 tsp. arrowroot starch I make a few tablespoons worth at a time and store it in a plastic container. I have also written the recipe on the container so I don't forget it! I actually found this recipe in a cookbook for what to do if you are in a pinch and don't have any baking powder and I just substituted the arrowroot starch for corn starch. Any starch would probably work.