Not sure the exact quantities as I'm not a precise cook but I'll try.
I peeled and sliced about 1/3 of a celeriac very thinly and arranged the slices in a small (1 pint) buttered casserole dish.
Then I added salt (1/4 tsp maybe) and 3/4 of a fat clove of garlic grated - both sprinkled over the top.
Poured on enough double cream to cover the celeriac - think about 200ml.
Finish with a little bit of ground nutmeg and covered with foil and into oven at 190.
After about 30 mins I took the foil off and let it brown. I think total cooking time of just under an hour.
Made enough for 2 people, it's very rich.