In a large, non-stick frying pan fry your pancetta and herbs in half the butter for 2 minutes, then add the garlic and parsnips. Cook for a further 3 minutes on a medium heat, until the pancetta is slightly golden and the parsnips have softened nicely. Cook your tagliatelle in salted boiling water (check the packet for cooking time), then drain, reserving a little of the cooking water. Mix the pasta with the parsnips and pancetta and stir in the rest of your butter and the Parmesan, adding a little of the cooking water to loosen the mixture and make it creamy and shiny. Season to taste.