Simple to make up to two days in advance, Peter’s sharp citrus and berry tart is perfect for a dinner party dessert.
Make the pastry. Tip the hazelnuts into a food processor and blitz until finely ground. Add the flour, butter, icing sugar and salt and pulse until the mixture resembles fine breadcrumbs. Tip into a mixing bowl, add the egg yolk and 1 tablespoon of water and mix with a round-bladed knife until the mixture starts to form clumps. Use your hands to gently knead until the dough comes together into a ball, then flatten it into a disc, wrap in cling film and chill for 30 minutes – 1 hour.
Lightly dust the work surface with flour, halve the chilled pastry and roll one half into a neat 22cm disc. Transfer to the lined baking sheet and press the tart ring into the pastry to make a 20cm disc. Leave the tart ring in place and prick the base with a fork.
Gather the trimmings with the remaining pastry half and, using your hands, roll it into a 65cm-long sausage. Using the rolling pin, flatten the sausage into a 4cm wide strip. Dust the pastry strip lightly with flour, roll it up along its length, and place it inside the tart ring.
Unroll the pastry against the side of the tart ring, pressing the edges down onto the base to seal and the sides neatly against the ring. Chill for 30 minutes. Meanwhile heat the oven to 200°C/180°C fan/400°F/Gas 6.
Neatly line the pastry with foil, fill it to the top with baking beans and bake for 15 minutes. Remove the foil and baking beans from the pastry case and return it to the oven for a further 10–12 minutes, until golden brown. Brush the inside of the tart with egg white and cook for a further 1 minute – this helps seal the pastry from the wet filling. Remove from the oven and set aside. Reduce the temperature to 170°C/150°C fan/325°F/Gas 3.
While the pastry case is baking, make the lemon filling. Measure 100ml of the lemon juice into a bowl, add the zest, sugar, double cream, eggs and egg yolk and whisk until combined. Carefully pour the filling into baked pastry case and bake for 16–18 minutes, or until the mixture is set but has a slight wobble in the middle. Allow to cool, then remove the tart ring.
While the lemon filling is baking, make the blackberry curd. Place the blackberries in a pan with the lemon juice. Cover and cook over a medium heat for about 5 minutes, until softened. Push the fruit through a sieve, pressing out the juice and pulp. Discard the seeds.
Return the blackberry purée to the pan and cook over a low–medium heat, until reduced to 200g. Add the egg yolks, whole egg and sugar, whisk to combine and place over a low heat, stirring continuously, until the curd is thick and reaches 75°C/167°F on a sugar thermometer. Remove from the heat and leave to cool for a few minutes.
Soak the gelatine leaves in a bowl of cold water for 3 minutes, until floppy. Drain them, squeeze out the excess water and add them to the curd, along with the cubed butter. Whisk to combine, then cover and cool slightly before pouring the curd over the lemon tart. Chill for 2 hours to set.
While the tart is chilling, make the candied lemon slices. Place the sugar in a small pan, add 50ml of water and cook over a medium heat for 1–2 minutes, until the sugar has dissolved. Add the lemon slices and simmer gently for 10 minutes, until the rind is tender. Drain and set aside. (You can dry them out on a wire rack in the oven at 90°C/70°C fan/200°F/Gas ½ for 1 hour if you like.)
Make the caramelised hazelnuts. Skewer each hazelnut on a cocktail stick or wooden skewer. Place the sugar in a very small pan over a medium heat. Cook, without stirring, until the sugar dissolves, then turns a deep, golden caramel. Slide the pan off the heat and plunge the base into a sink of cold water to stop the caramel cooking any further.
Take hold of the cocktail stick attached to the first hazelnut and swirl the hazelnut in the caramel until fully coated. Secure the open end of the cocktail stick under a heavy board on the edge of a work surface, with the caramel-coated hazelnut sticking out over the edge. The caramel should slowly drip into a fine tail (place a few sheets of kitchen paper on the floor to catch any drips). Repeat to coat all of the hazelnuts. Leave to set and harden before carefully removing the cocktail sticks.
Decorate the tart with fresh blackberries and edible flowers, the candied lemon slices and the caramel-coated hazelnuts.