That's the standard mix. I think they're better if you let the batter work overnight in the fridge. And of course you know all baking powder is not the same, find your favorite.
It doesn’t stay good forever either. Buy a new tin if in doubt.
What helps is keeping it covered, it sucks up moisture from the air like crazy. Take the lid off, measure out what you need, then lid on. No leaving it off while you do something else. I've got a small Calumet that's been opened for the best part of a year and I bet it's still good. But if the texture isn't right to the store 3 blocks away. Took a chance and made a great big cookie once.
