To make the pastry, process the flour in a food processor with icing sugar and butter until the mixture resembles coarse breadcrumbs. Add iced water; process just until the mixture comes together in a ball.
Turn pastry out onto a lightly floured work surface; knead it gently once or twice to form a ball and press into a 15-cm disc. Wrap in cling film and chill for 30 minutes.
To make the lemon filling, put the caster sugar and cornflour in a saucepan. Combine the lemon zest and lemon juice and the water and add to the pan. Stir constantly over a medium heat until mixture comes to the boil. Remove from the heat. Gradually pour the hot filling in a steady stream into the egg yolks, whisking constantly. Transfer filling to a bowl and cover with cling wrap; cool and then chill for about 2 hours.
Preheat oven to 180°C.
Roll out pastry to a 33-cm round about 5 mm thick. Line a 25-cm pie plate. Pierce the base several times with a fork. Chill the case for 15 minutes.
Line the pastry with baking paper and half-fill with dried beans or rice. Bake for 15 minutes. Remove the paper and beans or rice and cook for a further 10 minutes or until light golden and aromatic. Leave pastry case to cool, then spoon the chilled lemon filling into it, smoothing the top with the back of a spoon.
To make the meringue topping, beat the egg whites in a bowl with the cream of tartar until soft peaks form. Add sugar, a spoonful at a time, beating well after each addition. The meringue should be thick and shiny.
Spread the meringue over the lemon filling, making sure it forms a seal all around the pastry shell to prevent the filling from overheating, which could cause it to separate.
Bake for 10 minutes in the preheated oven or until the meringue is a light golden colour. Allow to cool before serving.