Before we crack on with the rice, we will rehydrate the porcini mushrooms. In a bowl with the dried porcini, add the boiling water then cover with cling film. Set aside.
Now let's start with the risotto. In a saucepan, sweat the onions by adding olive oil then the chopped onion and a pinch of salt. Cook on medium heat for a few minutes until turns translucent. We don't want them brown.
When the onions are done, add butter and then the risotto rice. Turn up the heat to toast the rice for about 2 minutes.
Then add the white wine. Let the alcohol evaporate, and the wine absorbed into the rice.
Now, add the stock about a ladle at a time while giving it a stir every couple of seconds. This will take about 18 - 20 minutes in total to cook. When you have run out of stock, you can add the water dried porcini was soaked into the risotto. You might not need all of the 250g.
While the risotto is cooking, fish out the rehydrated dried porcini and chop them up. Add it to the cooking risotto.
About 5 minutes before the risotto finishes cooking. In a separate pan, start with the mushroom garnish. In a very hot pan, add olive oil and the thinly-sliced mushroom. It is important that the pan is smoking hot, we want to enough heat to evaporate the water within the mushroom. If not, the mushrooms will start boiling in its juice and we certainly don't want that. After about 3 minutes, when the mushroom starts to dry out, season with salt and pepper then add the chopped garlic and parsley then turn down the heat to low. You can just keep the mushroom on the low heat while turning your attention back to the risotto. Just before the risotto finishes cooking, check the consistency that it's not too runny nor gloopy. When it had arrived at the right consistency, add the butter and parmesan. Taste and season with salt and pepper.
Spoon the risotto onto the plate. Garnish with the sauteed mushrooms and sprinkle over with a bit more parmesan then serve.