Roll out the pastry thinly on a lightly floured surface and use to line a 20 cm (8 inch) diameter x 5 cm (2 inch) deep loose-bottomed fluted flan tin, pressing into the sides. Trim the top and prick the bottom of the pastry case with a fork. Chill for 15 minutes, then line with nonstick baking paper, add macaroni or beans and bake in a preheated oven, 190°C (375°F), Gas Mark 5, for 15 minutes. Remove the paper and macaroni or beans and bake for a further 5 minutes until crisp and golden.
Put 75 g (3 oz) of the sugar in a bowl with the cornflour and lemon rind. Add the egg yolks and mix until smooth. Make the lemon juice up to 300 ml (½ pint) with water, pour into a saucepan and bring to the boil. Gradually mix into the yolk mixture, whisking until smooth. Pour back in the pan and bring to the boil, whisking until very thick. Pour into the pastry case and spread level. Set aside.
Whisk the egg whites in a clean, dry bowl until they form stiff peaks. Gradually whisk in the remaining sugar, a teaspoonful at a time, then keep whisking for 1–2 minutes more until thick and glossy. Spoon the meringue mixture over the lemon layer to cover completely and swirl with a spoon. Reduce the oven temperature to 180°C (350°F), Gas Mark 4, and cook the pie for 15–20 minutes until the meringue is golden and cooked through. Leave for 15 minutes, then carefully remove the tart tin and transfer to a serving plate. Serve warm or cold with cream.