Preheat the oven to 160°C/gas mark 3

Prepare the yeast butter before the other elements so it has time to set. Crumble the yeast onto a lined baking tray and roast in the oven for 40 minutes

Allow to cool, then transfer to the blender with the butter and malt extract. Blitz until smooth and combined, then scrape out onto a sheet of cling film. Roll into a log shape and leave to set in the fridge. Remove from the fridge and allow to soften slightly before using

Decrease the oven temperature to 130°C/gas mark 1/2

To make the parsnip purée, sweat the parsnips in an ovenproof pan with the butter. Add the milk, cream and a pinch of salt

Cover with a cartouche and cook in the oven until soft. Once cooked, transfer the contents of the pan to a blender and blitz until silky-smooth. Pass through a fine chinois for an even smoother finish, then set aside

Increase the oven to 180°C/gas mark 4

Wash the brill, removing the head and trimming the skirt with a sturdy pair of scissors

Now prepare the brine for the brill. Depending on how large your tray is, you'll need approximately 6–8 litres of water, plus 10% the weight of the water in salt. For 8 litres of water, you'll need 800g of salt, for 6 litres, 600g of salt, and so on. The exact quantities will depend on the size of the tray and the size of the fish – you'll need enough to completely submerge the fish in the brine

Once you've calculated your water and salt quantities, add them to the tray and mix until the salt has dissolved. Add the brill to the brine and set aside for 40 minutes

To make the potato galette, thinly slice the potatoes using a mandoline and place in a bowl of warm clarified butter. Season well with salt and pepper

Lay the potatoes neatly in a round baking dish, preferably a cast iron one, sprinkling each layer with thyme leaves and sliced garlic. When all the potatoes are used, cover with a sheet of greaseproof paper and place in the oven 45 minutes to 1 hour, until the bottom layer of the potato is golden and crispy

Remove the brill from the brine and pat dry. Place on a large baking tray lined with parchment paper, season with salt and pepper and drizzle with olive oil. Bake in the oven with the potatoes for 25 minutes

When the potatoes are ready, remove from the oven and leave to rest

When the brill is ready, remove from the oven and squeeze over some fresh lemon juice. Rest for a further 20 minutes before carving

Meanwhile, prepare the sourdough crumb. Place the bread in a blender and blitz to a fine crumb. Heat the butter in a pan and once foaming, add the breadcrumbs and cook until crisp. Drain on a tray lined with kitchen paper and set aside

Turn the potatoes out of the dish onto a board and brush with clarified butter. Cut a hole in the centre of the potatoes using a small round cutter and pipe the reserved parsnip purée in the centre. Finish with some picked thyme leaves and sourdough crumbs

Blanch the sprouts in salted boiling water for 5 minutes, until just cooked. It is important to ensure they are cooked properly to remove the bitter taste of an undercooked sprout

Once cooked, toss the sprouts in plenty of the yeast butter. Season with freshly ground black pepper and rock salt, then finish with some microplaned fresh chestnut and sourdough crumbs

Serve the rested brill on a large board or platter, and carefully portion at the table