It's cream of tartar, isn't it? Have you got any of that? If not, you can substitute some liquid for a more acidic liquid - vinegar or lemon juice or soured milk - if it's the sort of recipe that will let you do that. 3tsp lemon juice for 1tsp cream of tartar, I think, as a starting point.
It's cream of tartar, isn't it? Have you got any of that? If not, you can substitute some liquid for a more acidic liquid - vinegar or lemon juice or soured milk - if it's the sort of recipe that will let you do that. 3tsp lemon juice for 1tsp cream of tartar, I think, as a starting point.