Heat the stock in a medium saucepan and keep simmering. Strain the dried mushrooms and reserve the soaking water. Chop the fresh mushrooms and set aside.
Melt 55g/2oz of the butter with the oil in a heavy-based saucepan over a medium heat. Add the onion, garlic, thyme and bay leaf and cook until the onion is soft but not brown. Add the porcini or cep mushrooms and the fresh mushrooms and cook for a further 3-4 minutes.
Add the rice and stir until the grains are well coated with fat – about 3-4 minutes. Add the wine and stir until it has been absorbed. Add the reserved mushrooms soaking water and cook until this too has almost all been absorbed.
Add the warm stock, a ladleful at a time, allowing the rice to absorb the liquid each time before adding the next ladleful. Continue like this until the rice is tender but still a little firm to the bite. When the rice is ready, fold in the grated parmesan and stir. Garnish with chopped parsley and serve.