You technically can, but it changes the cookies. The Cream of Tartar is a raising agent, it adds a tart flavor andit keeps the cookies soft on the inside. If you absolutely want Snickerdoodles but don’t have cream of tartar, you can try using 3 teaspoons of baking powder instead of the cream of tartar AND the baking soda. It won’t give you the same old fashioned taste, but still a great cookie. You can also try adding 1/2 – 1 teaspoon of apple cider vinegar to the dough to add that tartness.