In a medium saucepan, heat the extra-virgin olive oil, a turn of the pan, and butter over medium to medium-high heat. Add the mushrooms and brown for 10 minutes. Stir in the thyme, shallots and garlic. Season with salt and pepper, to taste, and cook for 2 to 3 minutes more. Stir in the port or Marsala, the stock and the cream. Season the sauce with a little nutmeg, then reduce the heat and simmer until it is just thick enough to coat the back of a spoon. Cool completely and store in the refrigerator for a make-ahead meal. Reheat the sauce, covered, over medium heat until it bubbles, then reduce heat to low.
Bring a large pot of water to a boil over medium heat. Salt the water and add the pasta. Cook until al dente and then drain. Add the pasta to a large serving bowl.
Toast the nuts in small pan over low heat until fragrant. Add the warm sauce to the pasta and serve with cheese, nuts and chopped watercress on top.