This recipe is a little complicated to make, but is well worth the time spent. It is my most popular pie. Remember that a store bought frozen, pie shell does not hold as much filling as one in a regular pie plate.
In a 2-3 quart saucepan mix sugar, cornstarch and salt together, using a wire whisk. Still using whisk, gradually blend in cold water and lemon juice until smooth. Add beaten egg yolks, blending thouroughly. Using a silicone spatula, add boiling water gradually, stirring constantly. Add butter. Gradually bring mixture to a full boil, stirring gently and constantly with spatula over medium to high heat. Reduce heat slightly as mixture begins to thicken. Boil slowly for 1 minute after mixture comes to a boil. Remove from heat and stir in grated peel.
Pour hot filling into baked pastry shell. Let stand, allowing a thin film to form while preparing meringue.
For Meringue: Beat egg whites in a stainless steel bowl with an electric mixer until frothy (some fairly lare air cells still remain). Add cream of tartar. Beat on high speed until whites have lost their foamy appearance and bend over slightly, forming soft peaks when beaters are withdrawn (with mixer turned off). With mixer on medium speed, add sugar a tablespoon full at a time. When all sugar has been added, return mixer to high speed and beat until whites are fairly stiff but still glossy and soft peaks form when beaters are withdrawn.
Place meringue on hot filling in several mounds around edge of pie. Push meringue gently against inner edge of pie crust, sealing well. Cover the rest of the filling by swirling meringue from edge of pie to center, forming decorative peaks.
Bake at 350 degrees F. for 12-15 minutes, until golden brown.
Cool on wire rack at room temperature away from drafts for 2 hours before cutting and serving.
Note: It is easiest to get a nice cut through the meringue if you use sharp knife and dip into hot water after each cut.