1/Slice the onions and crush the fennel seeds. Cut the tips off the asparagus and put to one side. Finely chop the rest of the asparagus stalks. Finely chop the parsley.
2/ Put a large, high sided frying pan over a medium heat, and add the butter and onions. Fry gently for about 20mins until the onions are golden and caramelised. Remove them from the pan and set aside.
3/ Take the sausage meat out of the sausages (just use a sharp knife to score the skin and then peel it off) and fry it in the pan you just took the onions out of until it’s browned all over. Then add the fennel seeds, chilli flakes and lemon zest and cook for another minute or so.
4/ Put your pasta on to cook. Add the onions back into the pan along with the asparagus and cook for about 10 mins adding a couple of spoonfuls of the pasta cooking water.
5/ After 10 mins add the cream, another spoonful of the pasta cooking water and stir well. Drain the pasta and stir it through the sauce along with the chopped parsley.