Heat the butter in a large pan. Add the bacon and fry for 5 mins over a low-medium heat. Stir in the onion and fry for 10 mins more until the onion is soft but not coloured.
Stir in the mushrooms and continue cooking, stirring, for 5 mins. Stir in the rice and cook over a medium heat for 2 mins until the rice has started to turn translucent. Pour in the wine and allow it to bubble away over the heat.
Pour in a quarter of the stock and set a timer for 20 mins. Continue cooking, stirring very frequently, topping up with a splash more stock as it gets absorbed – this is best done in three more stages, until the rice is cooked and most of the stock has been absorbed (you may not need all the stock). The texture now should be creamy, like rice pudding.
Stir through the cooked chicken, warm briefly, then turn off the heat. Stir through the Parmesan and parsley, cover and leave to rest for 5 mins to allow more liquid to be absorbed into the rice. Season to taste and serve with extra Parmesan, if you like.