Place the mushrooms in a small bowl and cover them with 100ml boiling water. Set aside to soak. Pour the stock into a small saucepan, bring to the boil then reduce the heat to a gentle simmer.
In a separate pan, melt half the butter and add the onion. Cook, stirring, over a medium heat for about 6 minutes, until it's soft but not coloured.
Add the rice and stir for 2 mins, coating with the butter and onions. Pour in the wine, if using, and stir until it's evaporated. Add a ladleful of hot stock to the pan, and keep stirring until it has all but disappeared. Continue stirring in ladlefuls of stock until the rice is almost cooked and most of the stock used up (about 15-16 mins).
Meanwhile, heat the olive oil in a frying pan over a high heat and briskly fry the fresh mushrooms until golden. Keep warm. Remove the dried mushrooms from their bowl and roughly chop. Strain their soaking liquid and add it to the rice along with the soaked mushrooms. Cook away the excess liquid, then add the remaining stock with half the fried mushrooms. By now, the rice should be cooked but not mushy.
Remove the pan from the heat, stir in the remaining butter and the Parmesan, cover and leave to rest for 2 minutes. Serve in warmed bowls, topped with the remaining fried mushrooms, a scattering of parsley and extra grated Parmesan.