To make the pastry, put the flour, butter and ¼ tsp salt into a food processor and whizz until it resembles breadcrumbs.

Mix the yolk with ½ tbsp very cold water, add to the flour mix and whizz again. Add another ½ tbsp cold water if needed for the pastry to come together in a ball. Press this into a disc, wrap in cling film and rest in the fridge for 30 minutes.

Heat the oven to 200C/190C fan/gas mark 6.

Break the cauliflower into small florets, removing the tough core and the leaves – you can use those in a soup. Tumble the florets into a roasting tin with the thyme and bay leaves.

Season, grate over some nutmeg and add 1½ tbsp of the olive oil. Toss this around and roast the cauliflower for about 25 minutes, turning it over a couple of times, until tender. Remove from the oven and leave to cool. Turn off the oven; you’ll be using it again later.

Meanwhile, heat the rest of the oil and all the butter in a heavy-based pan and cook the onions over a medium heat at first, until they are softening, then season, add a splash of water and lower the heat.

Put the lid on – leave a little gap at one side – and sweat until completely soft. Make sure the onions don’t burn.

Remove the lid, whack up the heat and boil off some of the moisture so they aren’t too wet.

Put the spinach in a large saucepan with about 30ml water. Cover with a lid and cook on a low-medium heat for 4 minutes. Turn the spinach over and cover the pan again. Cook for another 4 minutes, or until the spinach has collapsed.

Leave to cool, then drain and squeeze the water out of the spinach between two dinner plates. It is very important that the spinach is dry, otherwise the moisture will stop the tart’s custard filling from setting. Chop roughly and season well.

Roll the pastry out on a piece of lightly floured baking parchment, into a 32cm circle. Use this to line a 26cm loose-bottomed tart tin that’s 3cm deep. Trim any overhang and wrap the scraps in cling film.

Prick the bottom of the pastry with a fork then chill in the fridge or freezer until firm and cold (this is crucial) – about 30 minutes.

Heat the oven again, to 200C/190C fan/gas mark 6, and put a metal baking sheet into it.

Line the pastry case with greaseproof paper and fill with baking beans.

Bake on the sheet for 10 minutes, then remove the paper and beans, and cook for another 8 minutes. Leave to cool.

Lower the oven temperature to 180C/170C fan/gas mark 4. Use the leftover raw pastry to patch up any little cracks you see.

Mix the whole eggs, yolks and cream together in a jug. Season and add some grated nutmeg and the Lancashire cheese.

Take the thyme and bay leaves out of the cauliflower. Spoon the cauliflower into the pastry case.

Mix the onions and spinach together, season and spread this over the cauliflower.

Pour the cream mixture on top of the vegetables. Sprinkle with the Parmesan. Return the tart to the baking sheet and cook for 40-45 minutes, or until the pastry is golden and the filling just set (it will go on cooking in the residual heat).

Cool for 15 minutes before transferring to a plate and serving.