Watercress Pesto with Linguine

0 Rinse the watercress and remove as many of you can of the thick stems.
1 In a food processor, add the watercress, garlic, parmesan cheese, and pine nuts and chop until it becomes a puree. Slowly add the olive oil while the motor is running the food processor.  You should have a creamy-thick green sauce
2 Meanwhile, cook the pasta in a large, salted pot and cook it to al dente, a couple of minutes before recommended manufacturer cooking time.
3 Save 1 cup of the cooking water. Drain the pasta and put it back into the cooking pot.
4 Add the butter and heavy cream. Mix well and once the butter is melted, add some of the watercress pesto. Mix well and serve on a pasta plate.
5 Add a spoonful of watercress pesto to each dish and top with parmesan cheese shavings.