In a large saucepan, combine sugar, cornstarch and salt. Gradually blend in cold water and lemon juice, Stir in egg yolks. Add butter and boiling water. Bring to a boil over medium-high heat, stirring constantly. Reduce heat to medium and boil for 1 minute. Remove from heat; stir in lemon peel. Pour into baked pie crust. Top with meringue, spreading all the way to edges sealing well. Bake at 350ºF for 12-15 minutes or until meringue is golden brown. Cool 2 hours before serving.
Meringue: In a large bowl with an electric mixer, beat egg whites with cream of tartar until foamy. Gradually add sugar, a tablespoon at a time, beating well after each addition until stiff peaks form.