Not the prettiest of vegetable, but do not hold that against it. To avoid wastage choose smoother celeriac. This dish is a variation of traditional potato dauphinoise, you could add sliced of potato and onion in-between the celeriac.
Preheat oven to 200 degrees C, gas mark 6.
Carefully half and slice the celeriac very thinly using a sharp knife.
Bring a pan of salted water to a rolling boil and par boil the celeriac for 10 minutes. Drain.
Rub the cut clove of garlic on the inside of an ovenproof dish. Spread the butter over the inside of the dish.
Layer the celeriac slices in the dish overlapping slightly and season.
Pour the milk and cream over the celeriac slices and top with the cheese and thyme. Bake for 20 minutes or until the celeriac is tender and the top golden brown.
Serve alongside roast turkey or goose.