A repost from the Witch’s Kitchen blog, which will soon go away.
I can’t tell you how many times I’ve started measuring out ingredients to bake something, only to discover I’m out of baking powder. Fortunately, it’s easy to make your own.
2 Tbps. cream Of tartar
1 Tbps. baking soda
1 Tbps. cornstarch
Sift ingredients together and store in small container with tight-fitting lid. Use measure for measure as commercial baking powder.