In a medium saucepan, combine sugar, cornstarch, flour, and salt. Gradually add water, stirring well. Cook over low heat, stirring constantly, until thickened and bubbly. Remove from heat and cool.
Gradually stir in beaten eggs to cooled mixture, stirring constantly. Cool 2 min over low heat, stirring constantly.
Remove from heat and add butter, lemon rind and juice, stir until butter melts. Cool slightly, spoon into pastry shells. Cool completely.
Garnish with a dollop of whipped cream and grated rind if desired.