Heat oven to 200C/180C fan/gas 6. Put the celeriac in a large saucepan, cover with cold water and season. Bring to the boil, then turn down to a simmer for 10 mins.

Carefully lift the celeriac out of the water and transfer to a large roasting tin. Arrange the thyme around the celeriac, drizzle over the honey and top with the butter. Bake for about 2 hrs, basting every 20 mins, until the celeriac has a golden glaze and feels tender when a knife is inserted into the middle.

Cut the celeriac into wedges, finely grate the raw mushrooms over the top, sprinkle with the parsley and drizzle with truffle oil, if you like.