Cream of Tartar
Beat egg whites and cream of tartar until foamy. On high speed, beat in sugar 1 Tablespoon at a time until stiff peaks form. Spread over filling, spreading to edge of crust to seal. Swirl into peaks.
Bake on lower rack at 325 degrees for 25 to 30 minutes (thermometer inserted in meringue will register 140 degrees.) Bake 3 minutes longer. Cool on rack up to 2 hours.