juice 2-3 lemon (about 100ml/3½ fl oz) and 2 tbsp lemon zest
To make the pastry, mix the flour and icing sugar in a bowl. Rub the butter into the flour with your fingers until crumbly. Mix in the egg yolks. If the pastry is still too dry, add 1-2 tbsp water until it comes together. Roll into a ball and divide in half (freeze one half for another recipe). Flatten out the pastry with your hands, wrap the dough in cling film, then chill for at least 30 mins. While the pastry is chilling, make the filling. Beat all the ingredients, except for the zest, together. Sieve the mixture, then stir in the zest.
Roll out the pastry on a lightly floured surface to about the thickness of a £1 coin, then lift into a 23cm tart tin. Press down gently on the bottom and sides, then trim off any excess pastry. Stab a few holes in the bottom with a fork and put back in the fridge for 30 mins.
Heat oven to 160C/140C fan/gas 3. Line the tart with foil and fill with rice or dried beans. Bake for 10 mins, then remove the tart tin from the oven, discard the foil, and bake for another 20 mins until biscuity. When the pastry is ready, remove it from the oven, pour in the lemon mixture and bake again for 30-35 mins until just set. Leave to cool, then remove the tart from the tin and serve at room temperature or chilled.