Edna Lewis started making her own homemade baking powder after becoming bothered by the chemical additives and tinny aftertaste of store-bought. The difference was subtle, but important—a cleaner flavor and a slightly better rise. Here is her formula:
To make 1⁄2 cup baking powder, Sift 1⁄4 cup cream of tartar, 2 tbsp. baking soda, and 1 tbsp. corn starch together 3 times. Transfer to a clean, tight-sealing jar. Store at room temperature, away from sunlight, for up to 6 weeks.