For the pastry:

1 Rub the flour and butter together until it resembles fine breadcrumbs. Add the icing sugar and salt and mix well. Add the egg and slowly bring the dough together.

2 Wrap the dough in cling film and chill for 30 minutes to an hour.

3 Roll the dough out to a large round and line a 23cm loose bottomed fluted tart tin. Prick the base of the pastry with a fork and place in the freezer for 20 minutes to chill completely.

4 Preheat the oven to 160 degrees and line the tart with parchment paper. Fill with baking beans or uncooked rice and bake for 15 minutes. Remove the parchment paper and cook for a further two to three minutes until the base is golden brown. Leave to cool.

For the lemon filling:

1 Put the lemon juice, zest, water and half of the sugar into a saucepan and heat until the sugar has dissolved. Set aside to infuse for 10 minutes, before straining into a new pan to remove the zest. Bring to the boil.

2 Whisk the egg yolks, remaining sugar and cornflour together in a bowl and slowly pour in the hot lemon juice, whisking all the time. Pour back into the pan and cook over a medium heat for three to four minutes until thickened and the cornflour starts bubbling. Remove from the heat and add the cubed butter, a little at a time, until it is all emulsified. Cool slightly.

3 Pour the custard into the cooked pastry case and leave to set at room temperature for one to two hours before transferring to the fridge to set completely.

For the Swiss meringue:

1 Put the egg whites, sugar and lemon juice into a bowl over a pan of simmering water. Using an electric beater, whisk for about five minutes until all of the sugar has dissolved and the whites are fluffy.

2 Remove from the heat and continue to whisk until cold, stiff and glossy.

3 Spread the meringue over the set custard and place under a hot grill for a few minutes to toast the meringue.