Prepare 1 litre of vegetable or meat stock (fresh stock is better but stock cubes will do fine). And keep it warm in its pot. Place the dried porcini in warm water to soak. Leave for 20 minutes changing the water a couple of times and keeping the water after the second rinse (the water will be used together with the stock to give more flavour to the risotto.
It is important not to take the porcini out of the water having attention not to touch the bottomo of the bowl as some sand might be dropped from the mushrooms and you really want to get rid of it and not put it back in the mushrooms.
Melt half of the butter with the oil in a deep pan. Add the chopped onion and stir fry until the onion is golden. Add 1/3 of the porcini and stir for 1 minute. Add the rice and mix it well for at least 5 minutes. This phase is crucial as the rice will absorb all the nice flavours from the base of the risotto.
Add the wine and stir till it's absorbed. At this point add the remaining porcini, salt and pepper. Add about a glass of stock and let it absorb and continue adding stock until the rice is cooked (approximately 15-20 mins).
Once the rice is cooked add the remaining butter, the parmisan and stir well. Finally add the chopped parsley and serve hot.