Soak the mushrooms in 1 cup of warm water for 1 hour. Remove and squeeze out excess liquid. Finely chop and set aside.

In a 12 to 14-inch skillet, place the guanciale and cook over medium heat until the fat has been rendered. Remove half the fat, add the olive oil, garlic and mushrooms and cook over medium-high heat until the garlic begins to color. Add the tomatoes and juices and cook over medium heat 20 minutes.

Meanwhile, bring 6 quarts of water to a boil and add 2 tablespoons salt.

Season the sauce with salt and pepper.

Cook the spaghetti in the boiling water according to package directions, until tender yet al dente. Drain the spaghetti, add it to the pan with the sauce and toss over high heat 2 minutes. Divide evenly among 4 warmed pasta bowls and serve immediately.