For a 28cm/11in pie:
For the pastry:
225g/8oz plain flour
25g/1oz icing sugar
100g/4oz butter
1 egg, yolk only
about 2 tbsp water
For the filling:
4 large lemons
75g/3oz cornflour
570ml/1 pint water
4 egg, yolks only
175g/6oz caster sugar
For the meringue:
5 egg, whites only
225g/8oz caster sugar

Method
1. Preheat the oven to 200C/400F/Gas 6.
2. To make the pastry, measure the flour and sugar into a bowl and rub in the butter until the mixture resembles fine breadcrumbs. Add the egg yolk and water and work to a firm dough - this may, of course, be done in a processor. Wrap in cling film and leave to rest in the fridge for about 30 minutes.
3. On a lightly floured work surface, roll out the pastry and use to line a 23cm/9in or 28cm/11in loose-bottomed, fluted flan tin. Prick the pastry lightly all over with a fork, line with greaseproof paper, fill with baking beans and bake blind in the preheated oven for about 20 minutes or until the pastry is pale golden and dried out, removing the paper and beans for the last 5 minutes.
4. Lower the oven heat to 150C/300F/Gas 2.
5. To make the filling measure 10fl oz/275ml cold water into a jug, and spoon the cornflour and sugar into a bowl. Add enough of the water to mix the cornflour to a smooth paste.
6. Pour the rest of the water, and the lemon zest into a small pan. Let this come to the boil then slowly pour it onto the cornflour, carefullly mixing it until you have a smooth paste.
7. Return the mixture to the saucepan and bring back to the boil, still mixing.
8. Simmer very gently for about one minute, stirring all the time to prevent it from catching. Then remove the pan from the heat and beat in the egg yolks, lemon juice and, finally, the sugar.
9. Pour the lemon mixture into the pastry shell and spread it out evenly.
10. For the meringue, whisk the egg whites in a large bowl with an electric whisk until they form stiff peaks. Whisk in the caster sugar, a spoonful at a time, whisking well and at a high speed between each addition. Spoon the meringue over the top of the lemon filling, spreading it out evenly and swirling it into peaks. Make sure there are no gaps.
11. Bake at the lower oven temperature for about 45 minutes for the 23cm/9in pie and about 1 hour for the 28cm/11in pie of until the meringue is crisp and pale beige on the outside and soft and marshmallowy underneath. 12. Serve warm or cold.