Sift the flour, powdered icing sugar, and salt into a large bowl. Add butter and rub until it resembles breadcrumbs. Stir in beaten egg and water to form a dough. Wrap in plastic wrap and refrigerate for 1 hour.

Remove dough from the fridge, cut into six pieces, and roll out until it's 2cm larger than your tart pan. Lift the dough into the tart tin, push to the sides, trim excess, and prick the base with a fork. Refrigerate for a minimum of 1 hour.

Preheat oven to 180°C (350°F). Line tart bases with parchment and fill with pie weights. Bake for 15 minutes, then remove parchment and weights and bake for another 15 minutes until golden brown. Cool completely before filling.

In a bain-marie, combine eggs, egg yolks, caster sugar, lemon juice, lemon zest, double cream, and cornflour. Whisk constantly until thickened, about 10-20 minutes.

Remove from heat, strain mixture through a sieve, discarding zest. Whisk in butter until melted. Cover with plastic wrap and refrigerate until fully cool.

Fill cooled tart shells with lemon curd and set in the fridge for 1 hour.

Whip egg whites in a medium bowl until frothy, then gradually add sugar, whisking until stiff peaks form and mixture is smooth and glossy.

Pipe meringue onto filled tart shells, then use a blow torch to scorch the tops until lightly browned. Optionally sprinkle with lemon zest and thyme leaves before serving.