• 2 knobs of butter
• 1 whole brill (about 1.5–2kg/3lb 5oz–4lb 8oz), gutted and cleaned
• 2 or 3 garlic cloves, peeled and sliced
• 2 tablespoons extra-virgin olive oil, plus extra for oiling
• 400–500g (14oz–1lb 2oz) celeriac, peeled and cut into 3–4cm (1¼–1½in) cubes
• about 250–300g (9–10½oz) hedgehog mushrooms (enough to fill a small basket), cleaned
• 1 small bunch of parsley, leaves picked and chopped
• salt and freshly ground black pepper

Heat the oven to 220°C/425°F/gas mark 7. Oil a large, flat roasting tray big enough to accommodate your fish, mushrooms and celeriac. Rub the base of the tray with half the butter, then season with some salt and pepper. Place the fish in the tray, scatter over the garlic slices, drizzle the fish with the olive oil, then give it a massage and season all over with salt and pepper. Scatter the celeriac cubes around the fish and add the mushrooms to the tray. I tend to leave them more or less whole, unless they’re really big, as they get cooked for the same amount of time as the fish and celeriac.

Dot the celeriac, mushrooms and fish with the remaining butter and season with a little more salt and pepper. Place the tray in the oven, and cook for 25 minutes, until the fish is cooked through (you can test this by inserting the tip of a small paring knife into the thickest part of the fish and seeing if the flesh comes away from the bone). Turn the mushrooms and celeriac once halfway through cooking.

Remove the tray from the oven and allow the fish to rest for 4–5 minutes before scattering with the chopped parsley and taking to the table straight away. Allow everyone to help themselves to a serving of fish and a scoop of the vegetables, straight from the tray.