Heat the oil in a large frying pan and fry the leek for around 5 minutes. Meanwhile, squeeze the sausage meat from the skins and crumble it into the pan with the leek. Fry over a medium to low heat until the meat is browned.
Add the red wine and let it evaporate for around 5 minutes, then stir in the wild fennel (keep a little for garnish) and some pepper. Let the ragu cook slowly over a low heat for around 30 minutes. Taste and add a little salt if necessary (Italian sausages tend to be quite salty so go easy).
Just before serving, stir in the ricotta and cream, if using, then add just-cooked pasta to the pan. Stir through and serve garnished with the reserved fennel and, if liked, some Parmesan on top.