Add the pistachios to the bowl of a food processor and process until very finely ground, about 2-2 1/2 minutes. Bring a large pot of generously salted water to a boil. Put a large saute` pan over a medium flame and heat the oil. Add the onion and sauté until soft, about 5-7 minutes. Add the pancetta to the pan and saute` until slightly crisp, about 5 minutes. Add the brandy and reduce the alcohol completely scraping up any bits at the bottom of the pan with a wooden spoon. Add the heavy cream and ground pistachios to the pan and stir to combine. Taste for seasoning and add salt and black pepper as desired. Cook the pasta until very al dente. Drain and add to the pan. Toss for 1-2 minutes and serve immediately. Sprinkle each dish with coarsely chopped pistachios.