Mix the flour and icing sugar in a large bowl. Rub in the cubed butter with your fingers until the mixture resembles breadcrumbs.
Add the egg and ice-cold water. Knead the mixture quickly into a cohesive dough.
Wrap the dough in cling film and leave to rest in the refrigerator for at least 30 minutes.
Meanwhile, preheat the oven to 180 degrees Celsius / 356 Fahrenheit with the top and bottom heat.
Roll out the dough on a floured surface until it is large enough to cover the base and sides of the pie dish.
Place the dough in the pie dish and press it gently into place. Prick the base of the dough with a fork.
Bake the dough blind (with parchment paper and baking beans) for 15 minutes. Remove the parchment paper and baking beans, then bake for a further 5 minutes or until the pastry is lightly golden brown.
Leave the dough to cool before adding the lemon filling.
To make the filling:
Heat the eggs, egg yolks, sugar, lemon zest, lemon juice and milk together in a saucepan, then add the cornflour and mix well with a whisk. Add the butter in pieces and mix until it has completely melted.
Continue whisking until the mixture starts to thicken. Then pour the filling onto the cooled base.
Leave the filling to set in the refrigerator for about 4 hours.
To make the meringue:
Beat the egg whites in a clean, grease-free bowl until soft peaks form.
Meanwhile, put the water and sugar in a saucepan.
Bring the sugar mixture to the boil, then leave it to boil without stirring until it reaches 115°C. You can use a sugar thermometer to measure this.
With the mixer running at a low speed, slowly pour the hot syrup into the bowl with the beaten egg whites in a thin stream.
Increase the mixer speed to high and continue beating until the meringue is shiny, stiff and completely cooled. This takes about 5–7 minutes.
Generously add the meringue as a topping to the cake. Brown the meringue with a blowtorch (or under the grill) and enjoy!