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.
In 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.
Cook 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.
This recipe was created by a contestant during a cooking competition. It has not been tested for home use.