I most often serve this sauce with pasta but, up until the stage that the butter and cream are added, it would also make the base for soup.
If using dried porcini, cover them in lukewarm water and leave to soak for at least 30 minutes. The strained liquid can also be added to the sauce and then cooked off until only the flavour is left.
1½ lb of cultivated mushrooms (including some shiitake if possible), sliced
Wild mushrooms – a couple of fresh or an ice cube size of cooked and frozen, or ¼ oz dried fungi, reconstituted as above
3 tbsps extra virgin olive oil
1 small onion, finely chopped
1 clove garlic
2 tbsps chopped flat leaf parsley
1 oz butter
4 fl oz double cream
freshly ground black pepper
3½ oz freshly grated Parmesan cheese
Heat the oil in a large frying pan and add chopped onion, cook gently until they are just beginning to take on some colour. If using reconstituted dried mushrooms, add these next, with their liquid, so that you can cook until all the liquid has been driven off. Then add the garlic and parsley and cook together for a minute. Now add the cultivated mushrooms and plenty of salt and pepper. The salt will help to draw liquid out of the mushrooms and you should continue the gentle cooking until this has simmered away, which will take about 10 minutes. Now add the butter and cream, turn up the heat, and boil until the cream has reduced by half. Toss the sauce with drained, freshly cooked tagliatelle and the grated parmesan cheese.