Rub the flour and butter together with your fingertips until the mixture looks like breadcrumbs. (A cool kitchen and cool fingers help.) Mix in the sugar. Add the egg and water and mix it in using a round-ended knife in a cutting motion until the ingredients come together into a dough ball.

Put the pastry ball on to a cool, floured work surface and lightly knead with the palm of your hand for a minute, to ensure a smooth pastry. Wrap and place in the fridge to rest for 40 minutes.

Lightly butter a 25cm push-up-bottom flan tin. Roll out the pastry on a lightly floured surface, then line the tin. Trim the edges with a knife and return to the fridge for 20 minutes to chill and relax.

Heat the oven to 180°C/gas 4.

Put the eggs, sugar, double cream and lemon zest and juice into a bowl and whisk well until creamy. Melt the butter and whisk it into the lemon mixture, then pour it into the chilled pastry case.

Carefully place the tart in the oven and bake for 15 minutes, then reduce the heat to 160°C/gas 3 and bake for a further 20 minutes or until the filling has set. Leave to cool for 1 hour before serving.