To make the pastry, put the flour, icing sugar and salt in a food processor and blitz briefly (or sift into a bowl).
Add the butter and blitz (or rub in with your fingertips) until the mixture resembles breadcrumbs.
Add the egg yolk and just enough milk or water to bring the mix together into large clumps.
Tip on to a lightly floured surface and knead very lightly to bring it into a ball.
Wrap or cover the pastry snuggly and chill in the fridge for 30 minutes.
For the filling, finely grate the zest from 3 lemons.
Juice these and 2 or 3 more lemons, then strain the juice into a measuring jug – you need at least 175ml lemon juice, and up to 200ml.
Whisk the eggs, egg yolks and sugar together in a bowl until well blended, then stir in the lemon zest and juice.
Leave to stand for about 10 minutes, then whisk one more time.
Leave for another 10 minutes.
Preheat the oven to 180°C/Gas 4.
Roll out the pastry fairly thinly and use it to line a 24cm tart tin, letting the excess hang over the sides.
Prick the base with a fork.
Line with baking parchment and ceramic baking beans (or dried beans or lentils), stand the tin on a baking sheet and bake for 15 minutes.
Remove the parchment and beans and bake for about 10 minutes more, until the pastry looks cooked – crispy, and very lightly golden.
Trim the excess pastry from the sides. Reduce the oven setting to 150°C/Gas 2.
Strain the filling into a clean bowl, skim off any surface froth, and stir in the cream until well combined.
Carefully pour into the tart case.
Bake for 30–35 minutes, or until barely set, with a slight wobble in the centre.
Leave to cool completely before serving, lightly dusted with icing sugar.
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