Bring a pan of water to a boil, add the pasta and return to a boil. Boil about 10 minutes until just tender. Drain well, then return the pasta to the hot pan.
Meanwhile, put the mascarpone, milk and tomato paste in a saucepan over low heat and stir until the cheese melts. Add the peas, basil and ham and stir 2 minutes until heated through. Season lightly with s