Some bakers like to add cornstarch to the egg whites to help them thicken. For the best possible texture and body, we use cream of tartar, which has acidity that helps to stabilize the whites. Also, avoid over or underbaking the pie. Either will ruin the meringue you worked so hard to make! Finally, the whites need to be very stiff, so don’t stop beating until the peaks can stand up on their own!