Heat the olive oil in a large heavy based frying pan over a medium heat. Fry the pancetta for 4-5 minutes, until starting to crisp. Add the onion, carrots and parsnip. Cook for 4-5 minutes or until soft. Add the garlic and cook for a further 2 minutes.
Add the mince, increasing the heat slightly, and cook for 4-5 minutes, stirring to break up the meat to ensure it has browned all over. Add the chopped tomatoes, beef stock, port and rosemary and bring to a simmer. Reduce the heat, partially cover and simmer gently for 1 hour and 15 minutes, or until the sauce has reduced and is nice and thick. Stir through the chopped chestnuts, season with black pepper and keep warm.
Meanwhile, cook the pasta according to the instructions on the packet. Drain and divide the pasta between four bowls. Top with the ragu and sprinkle with crumbled stilton.