First make the pastry, mix the flour, sugar and butter until it resembles breadcrumbs. Stir in the egg yolk to bind everything together and then wrap the pastry in Clingfilm and chill in the fridge for at least 1 hour.
Roll the pastry on a floured surface and line 4 individual tartlet tins with the pastry, then put these back in the fridge for another 30 minutes to chill.
To make the cherry compote, put the cherries, sugar, lime juice and zest into a saucepan and bring to the boil. Mix the water with the cornflour until smooth and stir into the cherry mixture. Cook gently over a medium heat for 2 minutes.
For the pastry cream pour 90ml of the milk into a bowl and blend together with all the egg yolks. Whisk in 45g of the sugar and all the cornflour.
Meanwhile pour the rest of the milk into a pot, stir in the cream, the remaining sugar and the vanilla seeds. Bring to the boil and pour the hot mixture onto the egg mixture, whisking all the time. Pour the mixture back into the pan and bring to the boil. Remove the pan from heat so it does not curdle and pass everything through a fine sieve and set aside to cool.
To make the tart filling, whisk the egg yolks, half of the sugar and lemon zest together until pale. In another bowl, combine the ground hazelnuts, cake crumbs and flour together and then fold into the egg yolk mixture.
Whisk the egg whites with a pinch of salt until frothy and then add in the remaining sugar and whisk for another minute. Gently fold the egg white mixture into the cake and egg mixture
To assemble the tartlet, spoon a layer of the pastry cream into each tartlet tin. Add a spoon of the cherry compote on top and cover everything with the hazelnut filling. Cook in the preheated oven for 15 to 20 minutes until golden brown.