1 1/2 ounces dried wild mushrooms, such as morels or porcini
3 tablespoons good olive oil
4 ounces pancetta, 1/2-inch-diced
3 cups chopped yellow onions (2 onions)
2 cups (1/2-inch-diced) peeled carrots (3 to 4 carrots)
2 cups (1/2-inch-diced) celery (3 to 4 stalks)
4 teaspoons minced garlic (4 cloves)
3/4 cup pearled farro (5 ounces) (See Recipe Note)
12 ounces fresh cremini mushrooms, cleaned, stems discarded, 1/4-inch-sliced
1/2 cup plus 2 tablespoons dry Marsala wine, divided
4 cups canned beef broth, such as College Inn
3 large sprigs fresh thyme, tied together with kitchen twine
Kosher salt and freshly ground black pepper
2 tablespoons all-purpose flour
2 tablespoons unsalted butter, at room temperature
4 ounces crème fraîche
1/4 cup minced fresh flat-leaf parsley
Place the dried mushrooms and 6 cups of water in a medium pot and bring to a boil. Turn off the heat, cover, and set aside for at least 20 minutes
Meanwhile, heat the olive oil in a large pot or Dutch oven. Add the pancetta, onions, carrots, and celery and sauté over medium heat for 10 minutes, stirring occasionally, until the vegetables are tender. Add the garlic and farro and cook for 2 minutes, stirring occasionally. Add the cremini mushrooms and the 1/2 cup Marsala and cook for 5 to 7 minutes, until the mushrooms have released some of their liquid.
Meanwhile, strain the dried mushrooms through cheesecloth, reserving the liquid. Coarsely chop the mushrooms and add them to the pot, along with the strained soaking liquid, beef broth, thyme, 2 teaspoons salt, and 1 teaspoon pepper. Bring to a boil, lower the heat, and simmer partially covered for 45 minutes, until the farro is tender. Discard the thyme bundle.
In a small bowl, mash together the flour and butter and stir into the hot soup. Simmer for 5 minutes, then stir in the crème fraîche and remaining 2 tablespoons of Marsala, and taste for seasonings. Sprinkle with the parsley and serve hot.