In large skillet over medium-high, add the butter and saute the onions until lightly browned, about 7 minutes. Add mushrooms, and salt and pepper, to taste, and cook for 3 minutes. Stir in the garlic and cook for another 2 minutes, then reduce the heat to medium. Add the stock and simmer until reduced by half. Stir in the pistachio nuts, chili flakes and oil, and season, to taste, with salt and pepper. Set aside.
In a separate pot, cook your favorite pasta (penne, pappardelle etc.) according to package instructions. Put the pasta in the center of each white plate and spoon some sauce over the top. Garnish with some grated cheese, and a sprinkle of chopped pistachios.
This recipe was provided by a chef, restaurant or culinary professional. It has not been tested for home use.