Cook the pasta in a large saucepan of boiling salted water until al dente. Drain and keep warm. Heat the oil over medium heat. Add the leek and cook until soft and golden.
Add the chilli and garlic and cook for a further minute. Add the wine, tomato puree and parsley and simmer for 5-6 minutes or until reduced and slightly thickened. While the sauce is cooking, prepare the pipis.
Heat a large, deep frying pan with 1cm water to simmering and add the pipis. Cover and cook for 3 minutes or until the shells have opened. Drain, reserving the cooking liquid, and discard any unopened pipis.
Add the cooking liquid to the tomato sauce and simmer for a further 3 minutes. Toss the pipis with the sauce and serve on top of the pasta with grated parmesan cheese if desired.