I’ve noticed that every recipe I’ve seen for lemon meringue pie calls for cream of tartar. Is it really necessary to use that ingredient? —J.D., Downers Grove, IllinoisCream of tartar is used in meringues to provide stability to beaten egg whites. It does increase the firmness of the meringue; however, you can still make a successful lemon meringue pie without it. Just take these precautions: Make the meringue on a dry day—humidity will add unwanted moisture and can make a real difference in the outcome of your product. Choose a clean deep glass or metal mixing bowl, and gradually add the sugar after the egg whites are foamy.