Dried mushrooms give a great, concentrated wild mushroom flavor to dishes that packs more punch than you get from fresh button mushrooms and even some fresh wild mushrooms.
Dried porcini are a popular ingredient in pasta sauces. bushwickgirl likes CHOW's Tomato-Porcini Sauce, but makes it with whole canned tomatoes in juice and a little tomato paste. Norm Man recommends this simple fettuccine with wild mushroom sauce.
nomadchowwoman uses dried porcini in a cream sauce for pasta: Saute pancetta or prosciutto, fresh mushrooms, shallots, and garlic, then add the mushroom soaking liquid and reduce, and finish with a bit of cream.
A handful of dried porcini tossed in simmering stock "makes the most wonderful base for a cream of mushroom soup," says eight_inch_pestle, "especially if you start with a double stock and then reduce the liquid by half or more while the mushrooms are in the pot."
A simple but tasty way to prepare whole dried shiitakes is to soak them, squeeze out the extra liquid, trim off the stems, and sauté them in butter, says tastesgoodwhatisit. Dried shiitakes star in CHOW's Mushroom and Pancetta Soup, an unconventional twist on simple Japanese soups.