Melt the butter in a large pan and add the mushrooms. Cook until the mushrooms are brown and tender. Add the scallions and garlic and saute until tender. Add the flour and cook for 1 to 2 minutes, then reserve.
02In a food processor, add the chicken stock, cream, gruyere, Parmesan, marsala, rosemary, thyme and roasted garlic, and pulse until well combined. Put the mixture in a pot over low heat and cook until the cheese is melted. Add the cream mixture to the mushrooms, season with salt and add the truffle oil.03Cook the pasta to 1 minute shy of al dente. Toss the cooked pasta with the mushroom sauce. Add the shrimp and cook until cooked through. Serve topped with celery leaves and toasted pine nuts.