To prepare the pudding, mix the sugar, cornstarch, and salt in a heavy saucepan. Pour in the water, stirring to combine. Warm the mixture over medium-low heat, stirring constantly until hot but short of boiling. Place the egg yolks, lemon juice, and zest in a small bowl and gradually add about ½ cup of the hot mixture to the yolks. Stir the egg mixture back into the sauc