Heat the oil in a deep frying pan and cook the onion and bacon for 5 mins to soften. Add the mushrooms and cook for a further 5 mins until they start to release their juices. Stir in the rice and cook until all the juices have been absorbed.

Add the stock, a ladleful at a time, stirring well and waiting for most of the stock to be absorbed before adding the next ladleful. It will take about 20 mins for all the stock to be added. Once the rice is cooked, season and serve with grated Parmesan.