Preheat the oven to 180C/350F/Gas 4.
Place the dried mushrooms in a bowl, add the boiling water to the bowl and leave to soak for ten minutes. Meanwhile, heat the olive oil in a medium sized ovenproof saucepan or casserole dish and cook the onion and garlic for a few minutes until soft and a little golden. Season with salt and freshly ground black pepper.
Drain the excess liquid from the mushrooms into a clean bowl. Chop the mushrooms, and add them to the garlic and onions along with the rice, chopped thyme and mushroom-soaking liquid. Pour the stock and the wine into the pan and bring the mixture to the boil. Season to taste with salt and freshly ground black pepper.
Cover with the mixture with a lid and place it in the oven. Cook for 15-20 minutes, or until the rice has just cooked and all the liquid has been absorbed.
Stir in 50g/2oz of the grated parmesan.
To serve, sprinkle with the remaining parmesan and thyme leaves.