Preheat the oven to Gas 3, 170°C, fan150°C.
Peel, quarter and thinly slice the celeriac.
Bring the crème fraîche and milk to the boil and add the celeriac and crushed garlic. Simmer gently for 3-4 minutes, stirring every so often so the celeriac doesn't stick to the pan.
Spoon into an ovenproof dish. Press the celeriac down as you go and scatter the thyme in between layers. Top with the cheese and bake for about an hour and a half until golden and bubbling. Serve with roast beef, chicken or steak.
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