If you get in a real pinch, you can make the meringue without cream of tartar. However, the cream of tartar keeps the egg whites from becoming runny, so it’s worth a quick trip to the store if you don’t already have it in your pantry.
When adding the sugar to the egg white mixture, watch the meringue closely! You want the peaks to be foamy and stiff, but not dry. Test it every 30 seconds or so while beating to avoid over mixing the meringue.