For the pastry:
175g cold butter
225g plain flour
70g icing sugar
2 medium egg yolks
For the filling:
300g blanched hazelnuts
250g butter, cut into cubes
150g caster sugar
3 medium eggs
1 vanilla pod, seeds scraped out
225g blackberries, plus extra to decorate
Preheat the oven to 200c/Gas mark 6. You will need a 27cm tart tin.
To make the pastry, put the butter, flour, icing sugar and egg yolks in the food processor and blitz briefly until a soft dough is formed. Tip out onto a sheet of clingfilm and form into a rough ball, cover with cling film and squash the dough out, flattening it with your hand so that it cools evenly in the fridge. Rest in the fridge for at least 1 hour.
Lightly flour a surface and roll the pastry as thinly as possible. Lay it over the tart tin, pressing it to fit the sides, then trim the edges and put back into the fridge for 30 minutes.
Put in a piece of greaseproof paper, large enough to come up the sides of the pastry and fill with dried beans or pulses. Bake blind in the oven for 15-20 minutes until light golden, remove from the oven and take out the paper and beans. Turn the oven down to 180c/ gas mark 4.
For the filling, place the hazelnuts on a baking tray and toast in the oven for 8 minutes. Leave to cool, then blitz briefly in a food processor, so there is a mix of textures. Put aside.
Using an electric whisk, cream the butter and sugar together until light and fluffy, then add the eggs and beat until well combined. Then add the vanilla seeds and hazelnuts and mix well. Spoon the mixture into the pastry case and dot the blackberries evenly over the top – they will sink into the mixture as it cooks.
Bake in the oven for 30-35 minutes – check after 15 minutes and once the top looks firm and golden, cover with tin foil to prevent it from over browning.
Remove from the oven and leave to cool in the tin before turning out.
Serve with fresh blackberries and thick double cream