Preheat the oven to 325 degrees. The Meringue: Whip the egg whites until frothy. Add the cream of tartar and whip until stiff but not dry. (The peaks should stand but should lean over slightly when the beater is removed). Beat in the confectioner's sugar one tablespoon at a time. Do Not Overbeat! Beat in the vanilla. The Filling: Thoroughly beat the egg yolks. Sift the sugar, cornstarch and salt into a large saucepan. Gradually blend in the cold water and lemon juice. When the mixture is smooth, blend in the egg yolks and butter. Stirring constantly, add the boiling water. Bring the mixture to a full boil, stirring gently. As the mixture thickens, reduce the heat and allow to simmer very slowly for about a minute. Remove from the heat and stir in the lemon peel. Pour the mixture into the pre-baked pie shell. The Pie: Spread the meringue very thickly onto the pie over the filling. Bake 10 to 15 minutes, depending on the thickness of the meringue.