Combine the farro, chickpeas and porcini mushrooms in a strainer, rinse well and discard any very shriveled looking beans.
Pour into a large bowl and add the sage, thyme, parsley, bay leaf and 6 cups of water, cover and soak in the refrigerator for 8 to 24 hours
In a large stockpot, heat 2 Tb olive oil over medium heat. Add the onion and sauté for 5 minutes, stirring frequently.
Add the garlic and sauté for 30 seconds.
Add 1/4 Cup of the sherry and sauté for 1 minute, until liquid is almost evaporated.
To the stockpot add the soaked farro & bean mixture, along with the soaking liquid, plus 2 cups of water (or you can use 2 cups of stock or broth for an even richer soup).
Bring to a boil, cover and simmer on low heat for 1 hour. After 1 hour, add 1 teaspoon salt.
In a large sauté pan, heat 2 Tb olive oil over medium high heat. Add half the sliced mushrooms, making sure there is an even layer of mushrooms and that they are not crowded in the pan. Cook 1-2 minutes to let them brown, then stir or turn them with tongs to brown the other side.
Add 1/4 tsp salt, a splash of soy sauce, and 2 Tb of the sherry to deglaze the pan. Stir to scrape up any browned bits on the pan, then pour into the stockpot with the simmering soup.
Repeat with the second batch of mushrooms.
Continue to simmer the soup for 30 minutes, or until the beans are tender. Taste, season with salt & pepper as you like, add the vinegar and truffle oil.
Serve warm, with a dollop of crème fraiche or sour cream.
