Pre-heat the oven to 200 °C
Combine the cornflour and sugar in a medium sized saucepan.
Add the lemon juice and water to the pan. Stir until smooth.
Place the saucepan over a medium heat. Cook, stirring constantly until the mixture begins to boil and thicken. Reduce the heat to low and simmer for 1 minute.
Remove the pan from the heat and stir in the rind, egg yolks and butter.
Divide the lemon curd mixture between 4 x 1/2 cup ramekins or glass jars. Place the dishes onto an oven tray.
Add the egg whites to the bowl of a stand mixer and beat until soft peaks form.
Gradually add in the extra castor sugar and beat until the sugar has dissolved.
Spoon the meringue mixture over the lemon curd filling.
Bake for 5 minutes, or until browned lightly on top.