Preheat oven to 325F. Combine the eggs and 1/2 c. sugar in a small bowl. In a double boiler, mix 1/2c. sugar, cornstarch, salt, and water. Cook over boiling water until thick; stir constantly. Cover. Bring mixture to a boil; boil one minute. Stir occassionally. Spoon a little of the hot mixture into the egg yolk, stir quickly. Beat the egg yolk into the hot mixture. Cook two minutes; stir constantly. Remove the pan from the water; stir in the butter, lemon rind and juice. Pour into pie shell.
Beat the egg white and salt until foamy. add the vanilla, beat in remaining sugar 1 Tbsp. at a time; continue beating until stiff and shiny. Cover pie with meringue. Make sure there are no gaps and the edges are sealed with meringue. Bake until delicately browned, about 15 minutes.