Slice about 1cm/ ½ inch off the bottom of your celeriac and roll it on to that flat edge, so it’s nice and safe to slice. Slice and dice it all up into 1cm/ ½-inch-ish cubes.
Don’t get your ruler out – they don’t have to be perfect. Put a casserole-type pot on a high heat, add 3 good lugs of olive oil, then add the celeriac, thyme and garlic, with a little seasoning. Stir around to coat and fry quite fast, giving a little colour, for 5 minutes.
Turn the heat down to a simmer, add the water or stock, place a lid on top and cook for around 25 minutes, until tender.
Season carefully to taste and stir around with a spoon to smash up the celeriac. Some people like to keep it in cubes, some like to mash it, but I think it looks and tastes much better if you smash it, which is somewhere in the middle. You can serve this with just about any meat you can think of.