If you want to mix ahead of time and store no longer than one month, add 1 measure cornstarch note: i use teaspoons for measure amount, but it really depends on how much you need.
The cornstarch will help keep the other ingredients from absorbing moisture (this is what is used in manufactured baking powder).
If you have a recipe that calls for double acting baking powder, just use twice the amount.
Oh, one more thing, to check and see if the baking powder in your pantry is still active, stir 1 teaspoon into one-third cup hot water.
There should be immediate vigorous bubbling.
If no bubbling or bubbling is sporadic, the baking powder is past its prime.
Homemade baking powder starts to fizz and release carbon dioxide the minute it is added to liquid, it is very important that the oven be preheated and baking pans be ready before mixing batter.
