Cream of tartar is an important ingredient in snickerdoodle cookies, as it helps activate the baking soda and gives the cookies their signature tangy flavor. However, if you don't have the cream of tartar, there are still a few ways to make snickerdoodles. You can try substituting baking powder for the cream of tartar and baking soda. Use 2 teaspoons of baking powder for every 1 teaspoon of cream of tartar. The use of a lot of baking powder may alter the taste of the cookies. You can also try using lemon juice or white vinegar in place of cream of tartar. For each 1/2 teaspoon of cream of tartar, you can use 1 teaspoon of lemon juice or white vinegar. Using these alternatives may affect the flavor and texture of your cookies. I recommend following the recipe as it is written in the recipe card for the best results.