Method

• 1.
  For the pastry, pulse the flour, butter and a pinch of salt in a food processor to the consistency of breadcrumbs. With the motor running, steadily add the water, stopping as soon as the dough comes together (you may not need all the water). Transfer the dough to a work surface, knead it a couple of times, then wrap and chill in the fridge for at least 30 minutes. (If you don’t have a food processor, place the flour, butter and salt in a mixing bowl and use your fingertips to rub together. Gradually add the water, mixing with a table knife, then bring the pastry together with your hands, wrap and chill.
• 2.
  Place a large frypan on medium heat. Add the butter followed by the pancetta, then fry, stirring regularly, until the pancetta is beginning to crisp and brown a little around the edges (4-5 minutes).
• 3.
  Add the leeks to the pan, along with a couple of tablespoons of water, half the thyme, the zest of the half lemon and some salt and pepper. Stir well, then cover with a lid/foil and cook, stirring occasionally, for 6-8 minutes until the leek is just cooked. Squeeze in the juice of the half lemon, then remove the pan from the heat and leave to cool.
• 4.
  Heat the oven to 200°C. Roll out the chilled dough on a lightly dusted work surface into a rough 30cm circle. Using the rolling pin to lift it, carefully unroll the pastry into a tart pan, working it gently into the edges and leaving any excess pastry hanging over the sides.
• 5.
  Prick the base all over with a fork, then line with baking paper and fill with ceramic baking beans or uncooked rice. Bake for 20 minutes, then remove the baking paper and beans/rice and bake for a further 5-10 minutes until the base is dry and lightly browned. Trim off any pastry overhanging the edges, then set aside to cool.
• 6.
  Whisk the eggs, yolks, cream and 100g of the ricotta in a large jug and season with salt and pepper. Arrange the leek and pancetta mixture over the base of the cooled tart case, then pour over the egg and ricotta mixture, dot over the remaining 50g ricotta, then arrange the lemon slices on top. Sprinkle with the remaining thyme, then bake for 35 minutes or until the filling is set and a little blistered on top. Leave to cool for at least 25 minutes before serving.