Step 1
Sift the flour, salt and sugar into a large mixing bowl and rub in the Trex with your fingertips until the mixture looks like fine crumbs. Add the egg yolk and 2-3 tbsp chilled water and mix with a round-bladed knife until the pastry clings together. Form the dough into a ball, then wrap and chill for 10 minutes.

Step 2
Preheat the oven to 200°C/fan oven 180°C/Gas Mark 6.

Step 3
Roll out the pastry on a lightly floured surface and use it to line six 10cm (4in) individual tartlet tins. Line each one with a piece of crumpled foil and bake ‘blind’ (i.e. without a filling) for 10 minutes.

Step 4
For the filling, beat together the egg yolks and condensed milk with the lemon and lime zest and juice. Remove the foil from the pastry tarts. Share the filling between them and return to the oven to bake for 5 minutes.

Step 5
Meanwhile, whisk the egg whites in a large grease-free bowl until they hold their shape. Whisk in the sugar until glossy. Share the meringue between the tarts and bake for 4-5 minutes, until golden brown.