Put the dried mushrooms in 6 cups of water in a medium pot and bring to a boil. Turn off heat and set aside for at least 20 minutes so they can re-hydrate
Heat olive oil in a large Dutch Oven
Add pancetta, onions, carrots and celery – saute over medium heat until the vegetables are tender, stirring occasionally, about 10 minutes
Add garlic and barley and cook for 2 minutes, stirring it a bit more
Add the fresh mushrooms and the Marsala, cook for 5-7 minutes
Strain the dried mushrooms, reserving the liquid
Chop the mushrooms and add them to the pot with the soaking liquid, thyme, salt and pepper
Bring to a boil, lower the heat and simmer for about 35 minutes, discard the thyme
In a small bowl, mash the butter and flour together and stir into the hot soup
Simmer for a few minutes, then stir in the creme fraiche