On a lightly floured board roll out the pastry or use a ready-rolled sheet. Line a 23cm flan ring or pie dish and trim away any excess pastry. Chill for 10 minutes.
Put a crumpled sheet of baking paper or tinfoil into the pastry case and fill it with dry chickpeas, rice or beans. Bake the pastry case for 15 minutes, and then remove it from the oven and carefully take out the paper and the beans. Return the case to the oven for 5 minutes to dry the pastry. The pastry must be thoroughly cooked and crisp.
While the pastry is cooking make the filling and topping. Combine the cornflour, lemon zest and juice in a saucepan and mix until smooth, then add the cold water. Cook gently, stirring until the mixture boils and becomes thick and clear. Stir in the sugar, egg yolks and butter and mix well.
Beat the egg whites until stiff but not dry. Beat in the sugar a spoonful at a time, until very thick and glossy.
Pour the filling onto the cooked pastry base and spoon the meringue topping over the filling, taking it up to the pastry edge, but not over it. Swirl into points and tips.
Bake for 15–20 minutes or until the meringue is lightly golden. Serve warm or at room temperature.
Add the pulp of 2–3 passion fruit to the lemon filling.