Method

1. In a bowl mix together the plain flour, pinch of salt, and the butter with a round bladed knife, then rub between fingertips until it resembles breadcrumbs. Mix 2 egg yolks with 2 tbsp of cold water. Stir into the butter and flour until combined. Bring together lightly in your hands and wrap in cling film or paper and leave to rest in the fridge for at least 30 mins. This can be done in a food processor if you have.
2. Heat the oven to 180c (fan) with a flat baking sheet on the middle shelf. After half an hour, roll out the pastry and use it to line a 22cm round 4 cm deep fluted loose bottom tart tin. Chill again if you have time, if not, prick the base with a fork, line the pastry case with baking parchment and fill with baking beans, bake in the oven for 15 minutes. Remove the paper and beans and glaze with an egg yolk. Bake in the oven for a further 5 minutes until golden and crisp. Remove from the oven and allow to cool.
3. While the pastry case is cooling, cover the potatoes with water and bring up to the boil and cook for 15 minutes until tender. Once cool slice into 0.5cm slices.
4. Place 1 tbsp of olive oil into a pan and cook the watercress for 2 minutes, until wilted. Remove into kitchen paper and squeeze out the excess water, leave to one side to cool, then roughly chop and season.
5. Lower the oven to 150c (fan). Mix the cream and eggs with a good grind of cracked black pepper and sea salt. Layer the potatoes, wilted watercress and taleggio into the pastry case and pour over the cream and egg mixture. Grate over the Parmesan and place on the pre-heated baking sheet in the oven to cook for 1 hour, until set with a slight wobble, or a toothpick comes out clean.
6. Top with dressed watercress and serve.