Step 1

Preheat the oven to 190C/170C Fan/Gas 5.

Step 2

To make the pastry, sift the flour and salt into a bowl. Rub in the butter using your fingertips until the mixture resembles fine breadcrumbs. Stir in the sugar.

Step 3

Add the egg yolks and then the cold water, a little at a time, using a table knife to bring the pastry together. If the mixture is too dry to hold together, add a little more water. Do not overwork the pastry or make it too sticky or it will become tough. Shape into a disc, cover with cling film and place in the fridge for at least 10 minutes.

Step 4

Unwrap the pastry and roll it out on a lightly floured surface to a large circle about 3mm thick.

Step 5

Transfer the pastry on the rolling pin to a 23cm/9in loose-bottomed tart tin, pressing it into all the corners and allowing excess pastry to hang over the edge. Chill in the fridge for 10 minutes.

Step 6

Place the lined tart tin on a baking sheet. Line the pastry case with baking paper and ceramic baking beans or dried beans. Bake for 15–20 minutes. Remove the beans and paper and bake for a further 5–8 minutes, until pale golden. Leave to cool. Trim off the excess pastry with a sharp knife.

Step 7

To make the filling, combine the cornflour and sugar in a saucepan, then stir in the lemon juice and 300ml/10½fl oz water until smooth. Bring to the boil, stirring frequently, until the mixture thickens. Reduce the heat, simmer gently for 1–2 minutes, then remove from the heat and immediately stir in the egg yolks. Leave to cool a little.

Step 8

Stir in the lemon zest and butter and mix until combined. Pour it into the pastry case and set aside to cool completely. The mixture should be smooth, thickened and set.

Step 9

To make the meringue, put the sugar and 75ml/2½fl oz water into a saucepan and gently bring to the boil, stirring until the sugar is dissolved. Cook until the sugar syrup reaches 120C on a thermometer.

Step 10

Meanwhile, put the egg whites into a free-standing mixer with a balloon whisk. When the syrup reaches 110C, start whisking until stiff peaks form when the whisk is removed. Once the syrup reaches 120C, while the mixer is whisking, pour it over the egg whites. Be careful not to pour it over the mixing attachment, which could splash it back at you. Whisk until the meringue is cool – it should be shiny and stiff.

Step 11

Remove the cooled tart from the tin. Spoon the meringue over the top, making sure there are no gaps and spreading it out so it just touches the pastry (this will stop it sliding off). Use the spoon to make it smoothly swirled or to create peaks all over.

Step 12

Using a blowtorch, gently caramelise the meringue. Alternatively, you can do this under a preheated grill for a few seconds. Serve.