Keeping a pack of egg white powder in the storecupboard for meringues saves you having a surplus of egg yolks to use up. The lemony filling can be baked a day in advance but make the meringue topping on the day of serving.
250g (9oz) homemade or bought sweet dessert pastry
A little flour for dusting
4 medium eggs
250g (9oz) caster sugar
finely grated zest and juice of 4 lemons
100g (4oz) unsalted butter, diced
For the meringue:
2 sachets Dr. Oetker Egg White Powder
150g (5oz) caster sugar
1. Preheat the oven to 200°C/400°F/Gas Mark 6. Thinly roll out the pastry on a lightly floured surface and use to line a 23cm (9inch) round, loose base tart tin, trimming off the excess around the edges. Line with greaseproof paper and fill with baking beans (or use dried beans reserved for the purpose). Bake blind for 20 minutes. Remove the beans and paper and bake the pastry for a further 5 minutes.
2. Beat the eggs with 100ml (3 1/2fl oz) water and pour into a saucepan. Add the sugar, lemon zest and juice and butter. Heat gently, stirring, until the butter has melted and the sugar dissolved. Strain through a sieve into the pastry case and carefully transfer to the oven. Bake for about 20 minutes until the filling is lightly set. Raise the oven temperature to its highest setting.
3. For the meringue, tip the sachets of egg white powder into a bowl and gradually blend in 120ml (4fl oz) warm water until smooth. Beat with a hand held electric whisk until softly peaking. Gradually beat in the sugar, a tablespoonful at a time, beating well between each addition until the meringue is thick and glossy.
4. Spread the meringue over the lemon filling, peaking it lightly with a palette knife. Return to the oven for a few minutes until the meringue peaks are golden. Watch very closely as the meringue with brown very quickly. Leave to cool before serving.