Step 1Bring a large pot of salted water to a rolling boil. Cook the pennette according to the package directions until al dente.
Step 2While the pasta cooks, melt the butter in a large deep skillet over medium heat. Add the leeks and a dash of sea salt and cook, stirring, until very soft, about 4 minutes. Add the cream and heat to a simmer.
Step 3Drain the cooked pasta well in a colander and immediately turn it out into the skillet with the leek mixture. Add the Gorgonzola and toss until coated. Add the pistachios and salt and pepper to taste. Continue stirring until well mixed. Serve at once, with freshly grated Parmigiano-Reggiano, if desired.