Begin by making the pastry as described in shortcrust pastry, sifting in the icing sugar into the rubbed in mixture then adding the yolk with the water before making the dough. Click here for Shortcrust Pastry. Then leave it to rest in a polythene bag in the refrigerator for 30 minutes.
Meanwhile, make the filling, grate the zest from the lemons, and squeeze enough juice to give 225 ml. Now break the eggs into a jug, and add the sugar to the eggs and whisk to combine, but don't overdo it or the eggs will thicken.
Next add the lemon juice and zest followed by the cream, and whisk lightly.
Roll the rested pastry as described in the basic pastry recipe to 30cm in diameter then carefully roll the pastry round the rolling pin and transfer it to the centre of the tin.
Now, using your hands, gently press the pastry into the tin to line the base and sides making sure you ease the pastry into the corners and press it against the sides then trim off any excess pastry around the top edge with a sharp knife.
After that use your fingers again to press the sides all round to the pastry so it is slightly proud of the tin.
All you now need to do is prick the base all over with a fork, as this will release any trapped air, which is what causes the centre to rise up. Then pop it in the freezer to chill for 30 minutes.
To cook the pastry base, pre-heat the oven to 190°C, gas mark 6 and place the baking sheet near the centre to preheat as well.
Once the pastry case is frozen put it on a flat surface. Place the piece of foil over it then press it down over the base and up the sides of the pastry.
Then turn the edge of foil inwards and crumple it against the sides to create a support that will hold the pastry in place whilst it cooks.
Put the pastry case onto the pre-heated tray in the oven and bake for 15 minutes.
Then remove the pastry case from the oven and ease the sides of the foil inwards and carefully lift it away from the pastry case (you can reserve this foil liner to use another time). Brush the base and sides all over with beaten egg (use a little from the filling), which will provide a sort of moisture proof coating so that the pastry stays beautifully crisp even after the filling has gone in.
Now return the pastry case to the oven for 7-8 minutes then, as you remove it, turn the temperature down to 180°C, gas mark 4.
Now pour the filling into the tart case. (If your prefer you can pour the filling from the jug and place the pastry case on the baking sheet in the oven, and then pour the filling straight into the pastry which avoids having to carry the tart to the oven and spilling it).
Bake on the baking sheet for about 30 minutes or until the tart is set and feels springy in the centre.
Let it cool for about half an hour if you want to serve it warm. It's also extremely good served chilled.
Either way, dust it with icing sugar just before serving and serve with well-chilled crème fraîche.