Peel the celeriac (keep the skin), then cut a ‘steak’ that’s about 8-10cm thick from a cross-section of the middle. Save the other two celeriac pieces. Put the celeriac steak in a saucepan and just cover with cold, salted water. Bring to the boil, then reduce to a simmer and cook for 12 mins. Carefully lift the celeriac out of the water (keep the water).

Heat the oven to 200C/180C fan/gas 6. Score the faces of the celeriac steak in a criss-cross, if you like. Heat the butter in an ovenproof frying pan until sizzling, then gently fry one side of the celeriac steak for 10 mins, until well browned. Flip it over, drizzle with the maple syrup and arrange the thyme around the steak. Bake for about 1hr 30mins, basting every 20 mins and turning it twice, until the celeriac has a dark glaze and feels tender when a knife is inserted into the middle.

Meanwhile, make the creamed celeriac and gravy. For the creamed celeriac, chop the celeriac offcuts into chunks and tip them into the reserved celeriac water. Bring to the boil and simmer for 10 mins, until soft, then use a slotted spoon to lift the celeriac out into a bowl (still keeping the water). Add the crème fraîche to the bowl, mash well, then season with salt, a pinch of cayenne and a grating of nutmeg. Set aside. If you want to be fancy, blitz with a hand blender or processor instead to make a smooth purée. Tip into a saucepan to reheat when needed.

To make the gravy, finely chop the reserved celeriac skin. Melt the butter in a frying pan, add the celeriac skin, onion and herbs, then fry for 15 mins, until the vegetables brown. Scatter over the sugar and continue to cook until sticky and caramelised. Stir in the flour until sandy, then add the Marmite and tomato purée. Cook to a sticky paste, then splash in the vinegar. Pour over about 400ml celeriac cooking water and add the stock cube and a splash of soy, then simmer everything together until you have a thickened sauce. Strain through a sieve into another pan or a jug.

About 10 mins before the roasted celeriac is ready, reheat the mash and gravy if needed. Bring the whole roasted steak to the table and carve into thick slices, or cut into quarters. Serve with the mash and gravy, then scatter with thyme leaves and finely grate some chestnut over, if you like.