For the strawberry juice and pulp, wash and halve the strawberries, and mix them with the sugar in a stainless steel bowl. Cling film the top and place over a pan of boiling water for two hours.
Pass the cooked strawberries through a sieve, keeping the juice and the pulp.
For the sorbet, place all the sorbet ingredients into a saucepan and bring up to a simmer, and cook for five minutes. Leave to cool then place into an ice cream machine and churn until frozen and set. Transfer to a freezer until needed.
For the sweet pastry, mix together the icing sugar, flour, vanilla and butter in a food processor until the texture of fine crumbs. Add four egg yolks and blend lightly until combined. Remove the pastry from the processor, wrap in cling film and leave to rest for two hours in the fridge.
Dust a work surface with flour and roll out the pastry to the thickness of a pound coin. Line a tart mould (roughly 35cm/14in length x 11cm/4½in width x 2.5cm/1in depth) with the pastry and place back into the fridge for an hour.
Preheat the oven to 160C/325F/Gas 3, bring the pastry out of the fridge and prick the base all over with a fork, bake in the oven for 15 minutes or until it starts to turn golden-brown. Lightly whisk the remaining egg yolk, remove the tart mould from the oven and while still hot brush the pastry all over with the egg yolk. Return the pastry to the oven for another five minutes. Then remove and set aside to cool.
For the elderflower and lemon tart filling, heat the cream and lemon zest in a saucepan until it begins to simmer. Whisk the mixture. In a separate bowl, whisk together the eggs and sugar.
Pour the hot cream over the eggs and sugar and whisk to combine. Allow the mixture to cool, then mix in the lemon juice and cordial.
Turn the oven down to 110C/225F/Gas ¼. Pour the lemon and elderflower mixture into the pastry case and bake in the oven for 20 minutes. The tart is done when it has just a slight wobble in the centre, if this isn’t the case, return to the oven and check every couple of minutes until this is achieved.
Leave to the tart to cool completely then remove from the mould.
For the vanilla meringues, preheat the oven to 110C/225F/Gas ¼. Whip the whites until stiff then add two-thirds of the sugar and continue to whisk for two minutes.
Add the final third of the sugar with the vanilla seeds and whisk for another 30 seconds. Fold the vinegar and cornflour into the meringue and place into a piping bag with a plain nozzle.
Line a baking tray with parchment paper and pipe out the meringue in 3cm/1in diameter blobs. Bake the meringues in the oven for 25-30 minutes, or until crisp but not coloured.
For the sugared strawberries, mix the strawberries with the sugar and vanilla in a bowl.
For the vanilla yoghurt, mix all the ingredients together in a bowl.
For the elderflower and lemon syrup, place all the ingredients into a pan and bring to the boil, simmer for two minutes.
To serve, place a slice of the tart in the centre of a serving plate, dot the meringues and fresh strawberries around. Place a spoonful of the sugared strawberries by the side of the tart and top with the sorbet. Finish with a few dots of vanilla yoghurt around and a drizzle of the syrup all over.