Key Lime Pie

1 baked pie shell
1 1/2 cups sugar
6 Tbsp. cornstarch
1 1/2 cups boiling water
3 Tbsp. butter
1 tsp. salt
4 Tbsp. lime juice
4 eggs, separated
1 tsp. baking powder
5 Tbsp. sugar

Beat egg yolks, add sugar, cornstarch and salt sifted together. Stir into boiling water and cook until thick. Add butter and lime juice. Pour into pie shell. Meringue: Beat 4 egg whites until they will hold a peak. Add baking powder and beat well, then add gradually the sugar; continue beating until glossy. Pile lightly on the filling being sure pie is entirely covered. Bake 15 minutes in a hot oven.