Preheat oven to 220˚C (200˚C fan-forced). Lightly grease the flan tin.

Combine cornflour, sugar, lemon juice, zest and water in medium saucepan. Stir until mixture is smooth. Heat over a medium-high heat, stirring constantly until mixture reaches the boil. Reduce heat to low and continue stirring for 1 minute, remove from heat.

Add butter and egg yolks to cornflour mixture and stir vigorously. Continue stirring until all the butter has melted and the ingredients are well combined. Pour filling into a small container, cover and refrigerate until cold.

Combine the contents of the pastry mix sachet, caster sugar and water and mix to stiff dough. Knead the dough on a lightly floured surface until a smooth ball forms, roll out to 3mm thick. Line the prepared tin with rolled pastry and trim any excess. Place a sheet of baking paper on top of the pastry and fill with pastry weights, dried beans or uncooked rice.

Bake for 8-10 minutes, remove weights and baking paper and bake for 5-10 minutes more, until the pastry is a light golden colour. Allow pastry shell to cool completely.

Place egg whites in a large bowl of an electric mixer and beat on high speed until at soft peak stage (when the beater is lifted, a peak will form and then droop over). Add the sugar gradually and continue beating until the sugar has dissolved and the mixture is thick, glossy and forms stiff peaks.

Spoon lemon filling into cooled pastry shell and spread evenly. Spread meringue to cover filling.

Bake for about 7-10 minutes or until meringue lightly browns. Allow to cool to room temperature then cover and refrigerate until cold.