Bring a medium pan of water to the boil over a high heat. Add the penne pasta and a little salt, and cook following the packet instructions, adding the peas for the last 3 minutes of cooking time. Meanwhile, heat a frying pan over a moderate heat. Cook the pancetta for 3-4 minutes until crisp, stirring often. Remove with a slotted spoon to a plate and drain on kitchen paper.

Drain the pasta, return to the pan and stir in the watercress, pancetta, creme fraiche and two-thirds of the Parmesan. Season to taste, sprinkle with remaining Parmesan and serve piping hot.