Place the dried porcini in a small pot and cover with four cups of water: bring to a boil. Shut off heat, cover pot, and allow porcini to soak for 20 minutes.
Meanwhile, heat the olive oil in a heavy-bottomed pot or Dutch oven.
Add the Canadian bacon or 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 sauté for 2 minutes, then add cremini mushrooms and Marsala and continue cooking for 5 minutes more.
Strain the porcini soaking liquid directly into the soup pot. Add the broth and the thyme.
Rinse the porcini under cold water, then coarsely chop them and add to the soup.
Add the salt and 1 teaspoon pepper, bring soup to a boil then partially cover and lower the heat to gentle simmer for 45 minutes.
Just before serving, mash butter and flour together and add to the soup. Swirl until combined.
Add another tablespoon or two of Marsala wine and more salt to taste, if desired. Sprinkle with parsley and serve.