For the risotto, heat the olive oil in a pan. Place the onions, garlic and a pinch of salt into the pan and cook until the onions are soft and transparent.
When the onions are cooked, add the rice and stir until the rice is very hot and the grains are starting to turn translucent. Begin to add the water little by little, stirring continuously. Cook for 18-20 minutes then remove the pan from the heat and leave to stand.
To complete the risotto, heat a little olive oil in a frying pan. Add the mushrooms to the pan and fry for a few minutes.
When the mushrooms have softened, mix them through the risotto base and cook the rice for a further few minutes. Once the rice is soft, stir in the parmesan, chervil, chives and tomatoes. Season with salt and freshly ground black pepper.
To serve, place the risotto into the middle of four serving dishes and drizzle over a little white truffle oil.