Make a celeriac stock by boiling celeriac peelings in a litre of water with a few sprigs of thyme for 10 minutes; strain and use here instead of the chicken or vegetable stock.
2 tbsp olive oil, plus extra for mushrooms
4 sprigs thyme, chopped
2 cloves garlic, crushed
2 cups diced celeriac
2 cups risotto rice
4 cups vegetable or chicken stock
2 tbsp unsalted butter
1/2 cup freshly grated parmesan cheese
2 cups mixed mushrooms , sliced
Heat a heavy-based saucepan over a moderate heat and add the oil, thyme, garlic and celeriac, stirring regularly until the celeriac begins to soften and the aroma intensifies. Add the rice, stir, then add the stock and cover.
Cook on a low heat for 12 minutes or until the stock is mostly absorbed and the rice is just cooked, then stir through a good pinch of salt, butter and cheese. Sauté the mushrooms in a little oil in a pan until golden brown.
Serve the risotto in warm bowls, topped with the mushrooms.