For the pie, place the flour, salt and butter into a bowl and rub together until the mixture resembles breadcrumbs.
Add the water a little at a time, until the mixture comes together as a dough. Knead lightly, shape into a thick disc, wrap in clingfilm and chill in the fridge for 30 minutes.
Preheat the oven to 180C/350F/Gas 4.
Dust the work surface with a little flour then roll the pastry out to a 5mm/¼in thickness. Cut out four 15cm/6in and four 10cm/4½in circles from the pastry.
Line each of four dariole moulds with the larger circles of pastry.
Mix the blueberries, sugar and vanilla seeds together in a bowl until well combined. Divide the mixture among the dariole moulds, pressing down firmly.
Brush the edge of the pastry with the beaten egg yolk then cover each mould with a 10cm/4in pastry circle. Press down the edges firmly and trim any excess. Crimp the edges and brush with the remaining egg yolk.
Bake in the oven for 30-35 minutes, or until the pastry is cooked through and golden-brown.
Remove the pies from the oven and set aside to cool for five minutes.
For the custard, whisk the egg yolks and sugar in a bowl until well combined.
Bring the milk and cream to the boil in a saucepan. Slowly whisk the cream mixture into the eggs until well combined. Return the mixture to the saucepan and heat slowly, stirring continuously, until the custard has thickened enough to coat the back of the spoon.
For the compote, heat a frying pan until hot, add the blueberries, sugar and water and cook for 2-3 minutes, or until syrupy.
To serve, spoon the custard in a pool in the centre of the plate then turn the pie out on top. Drizzle the compote around the plate and finish with a quenelle of clotted cream.