Place porcini into a heatproof bowl and pour enough boiling water to cover them. Set aside to cool. Drain the porcini, reserving the liquid.
Heat oil and butter in large saucepan over medium heat, add onion, garlic-saute for 3-4 minutes until soft, making sure you don't colour the onion. Add Swiss brown, button and flat mushrooms, cook for 8- 10 minutes or until the mushrooms have collapsed. Add the porcini and cook further 2-3 minutes.
Place another large saucepan of water over high heat and bring to the boil. Add 2 tablespoons of salt to water then the risoni and cook until just under al dente. Drain the pasta and add a little oil to the pasta to stop it from sticking.
Add the pasta to the mushrooms, and gradually add 1 cup of vegetable stock at a time, making sure your stirring constantly, so that stock is absorbed by the pasta. Reduce the heat to a simmer. Once you have added half the chicken stock to the pan, taste the pasta to see if the pasta is cooked. If so, add ¼ cup of the porcini liquid and stir to combine.
Remove from the heat, add parmesan, parsley and season. Spoon into bowls, drizzle with extra virgin olive oil and serve immediately.