about 1/2 cup
1/4 c. cream of tartar
2 Tbsp. baking soda
1 Tbsp arrowroot powder
Combine all ingredients in a large bowl and mix well. This recipe can be doubled to make a larger supply.
I started making my own baking soda because I was concerned about the aluminum and potentially-GMO cornstarch in commercial baking soda mixes. This one uses nutritious arrowroot powder (sometimes called arrowroot flour) in place of the cornstarch.