1 can sweetened condensed milk
4 egg yolks
1/2 c. key lime juice
4 egg whites
6 tbsp. sugar
1/2 tsp. cream of tartar

Mix together milk, egg yolks, and key lime juice. Beat 1 egg white until stiff and fold into previous mixture. Pour into baked pie shell. Beat 3 egg whites and gradually add sugar and cream of tartar. Spread over filling and bake until egg whites are golden brown.