I am following the Cook's Illustrated recipe for Snickerdoodles, which calls for a 2:1 ratio of cream of tartar to baking soda. They state explicitly at the very top of the recipe:
Cream of tartar is essential to the flavor of these cookies and it works in combination with the baking soda to give these cookies a lift. Do not substitute baking powder.
Unfortunately, I'm in Sweden and supermarkets do not sell cream of tartar, only tartaric acid (vinsyra).
Previously I've simply substituted baking powder (against their recommendation), but now I am wondering if would be possible to use that tartaric acid to get the "characteristic tangy flavor" that they describe. If so, how?