First of all, chop finely parsley, garlic and rosemary and soak the dried mushrooms in hot water for at least 20 minutes. Do not discard their water.
Dice the fresh porcini in medium size chunks.
Set all that aside and turn your attention to the onion, which has to be chopped finely, too. Heat up some extra virgin olive oil in a saucepan (if you have one of those old fashioned crock pots that go on the fire, even better!), then add the onion and the coarse salt; when the onion is lightly golden in color, add the garlic, rosemary and parsley previously prepared, along with the bay leaves. Add immediately the porcini and cook for about 15 minutes, stirring often.
While the fresh mushrooms cook, slice the dried mushrooms, which are now reconstituted after steeping in the hot water, and add them to the pan. In a bowl, mix together the tomato double concentrate (one tube, or little can, depending on which type or brand you usually get at your local store) and the dried mushroom water, until the concentrate is entirely dissolved.
Add it to the mushrooms and cook for 30 minutes on a medium heat, then turn it down to low and let the sauce simmer for another hour, stirring often.
And voilà, your sugo ai porcini is ready! If you fancy, you could add half a glass of red wine to it while it simmers, but if you do so, make sure to save only half of the dried mushrooms' water. This sauce is perfect with ravioli, fresh potato gnocchi and fresh pasta such as tagliatelle and Piedmontese "tajarin," fresh egg noodles. It is also delicious served with polenta and a sprinkle of grated parmesan on top.