In a medium saucepan, blend cornstarch and tap water. Add boiling water and cook over medium heat, stirring constantly, until thick and clear. Add sugar, lemon rind, and butter. Cool. Stir in eggs and lemon juice (lemons vary in size and juiciness; don’t skimp). Turn into unbaked pie shell. Cover with top crust spread with Crisco, milk, and a sprinkling of flour. Make vents. Bake at 425 degrees F for 10 minutes, then at 375 degrees F for 30 minutes.