Cook pasta in UN-salted water according to package directions or until al denté. Drain.
While pasta is cooking, melt the butter in a sauce pan over medium heat. Add the flour and whisk constantly until smooth, and cook for about 3-4 minutes or until mixture turns golden.
Add milk and cream and whisk until sauce begins to thicken, about 4 minutes. Add the gorgonzola and stir to melt. If sauce is too thick, add more milk, 1 tablespoon at a time until you get the right thickness.
Place pasta in bowls and drizzle with gorgonzola cream sauce, top with a handful of pistachios and sprinkle with parmesan and chocolate shavings. Serve immediately.