Heat the stock in a saucepan and let it simmer covered.
Heat the oil and butter. Steam the onions and mushrooms for about 5 minutes until the liquid has boiled away. Add salami and cook for another 3 minutes. Add the rice and stir for about 1 minute until it is completely coated with fat.
Pour hot stock into a ladle (125 ml) and heat the mixture at medium temperature, stirring constantly, until the rice has absorbed the liquid. Add more stock in a ladle and cook the rice for 20-25 minutes, stirring constantly, until it has absorbed all of the stock.