Whip together condensed milk and separated egg yolks until light and creamy at medium speed,about 8 minutes.Add 1/2 cup lime juice. Let rotate at low speed for about 1 second.Fold a few times with a rubber spatula.Pour into baked pie shell.Let stand. Beat separated egg whites with cream of tartar for a full five minutes.Add sugar.Beat another full five minutes.Spread on top of pie.Brown in oven at 350 degrees. ----