Here we go:
One large celeriac peeled and sliced as thin as you want it, obvs thicker may take longer to cook
Baking dish olive oiled
Sauce : 500ml double cream, Small splash milk and if wanted - dijon mustard, , 2 tsp
Garlic to taste, finely chopped
Thyme leaves
Process: whip together cream, milk and mustard if using. Layer celeriac in baking dish, salt/pepper + garlic/thyme between layers and pour cream mix over this. Put in pre-heated oven at around 150C, Gas 3. Bake for 90mins (?) or until celeriac is cooked.
Try not to eat it all first go. That's the hard bit.