When you run out of baking powder in the middle of a recipe, it isn’t always convenient to run to the store. Try mixing a 1/4 teaspoon baking soda, 1/2 teaspoon cream of tartar and a 1/4 teaspoon cornstarch in a small bowl and using it instead. It will give you the same results as 1 tsp of baking powder!
Please note that this recipe is the equivalent of 1 tsp of baking powder; adjust the recipe accordingly.
Visit Joy of Baking for more quick substitutions!