Squash, chestnut + black garlic tart with flaky walnut pastry

This is a centrepiece of a tart that that really makes a star of the beautiful wedges of roasted squash, so if you can find them, buy crown prince or onion squash, which will look amazing – though butternut will do. Shop-bought pastry can be used here too, but I encourage you to try this walnut pastry if you can. You will need a loose-bottomed 26cm fluted tart tin.

Serves 8

For the pastry
300g flour
50g walnuts
5 sprigs thyme
½ tsp flaky salt
175g cold cubed butter
1 egg, beaten with a splash of milk

For the filling
2 tbsp plain flour
3 eggs
200ml double cream
100ml whole milk
Salt and black pepper
Zest of 1 lemon
1 squash (about 1.2kg), cut into 2cm-thick wedges
1 pinch dried chilli
2 tbsp olive oil
Butter
2 large or 4 small leeks
Leaves from 1 bunch sage, roughly chopped
1 head black garlic
100g vacuum-packed chestnuts, crumbled
A few sprigs rosemary

Heat the oven to 190C (170C fan)/375F/gas 5. Whisk together the dry pastry ingredients, put in the bowl of a stand mixer with a hook attachment, add the butter and pulse a few times until you have a rough looking dough. Wwith the motor running, adding a tablespoon of very cold water at a time, and pulse again for four or five turns of the blade; keep adding water until the dough just comes together.

Take the lid off and pinch the dough with your fingers. Add a little more water if it feels dry, and keep blitzing until the dough comes together in a ball; it should be a buttery pastry and not feel overly crumbly. Wrap the dough in clingfilm or greaseproof paper and put in the fridge.

Meanwhile, make the filling. Whisk the flour into one of the eggs to make a paste. Add the remaining eggs one at a time, mixing well. Whisk in the cream and milk, then strain this mixture into a bowl to remove any lumps of flour. Season with the sea salt and plenty of cracked black pepper and grate in the lemon zest, then set aside.

Toss the squash with the chilli and oil, season, and bake uncovered for 30 minutes, then cover with foil and bake for another 15 minutes.

Meanwhile, fry the leeks gently in a little butter for 15 minutes, until soft and sweet, then add four of the sage leaves. Take off the heat, add the black garlic, and season well.

On a floured work surface, roll out the pastry to 3mm thick, then until it is an even £1 coin thickness and use the rolling pin to roll it on to the tart tin, using any leftover pastry to push the pastry into the tin. Line with baking paper, weight down with baking beans and blind bake for 12 minutes. Remove the paper and baking beans, brush the pastry with eggwash, and bake for another eight minutes.

Take the shell out of the oven, leave to cool a little, then add the leek mixture. Top with the squash, crumble over the chestnuts, and finally pour over the egg-cream mixture. Bake for 40-50 minutes, until set and golden brown on top.

Take out of the oven and leave to cool a little. Meanwhile, fry the rosemary leaves and remaining sage leaves in olive oil until crisp. Top the tart with the crisped herbs and serve.

Photo: Matt Russell