Remove the tough base of the asparagus peel the stalk and wash. Chop them up in small pieces, leaving the tips aside (about 3 centimetres) which will have to be finely sliced. Peel, mince and fry the onion lightly until soft with a knob of butter, melted previously in a saucepan. Next add the pieces of asparagus stalk; once lightly flavoured, pour a scoop of warm water and cook for about 10 minutes.In a mixer blast the mixture and place it in the already used saucepan, add salt and pepper to taste and simmer. In the meanwhile cook the pasta in plenty of boiling salted water. Just before draining the pasta, remove the sauce from the heat, blend the ricotta well pressed or passed through a strainer, a sprinkle of ground pepper and the asparagus tips finely sliced; put it over the heat for a few seconds and then switch off the heat. Drain and moisten the farfalle and add to the sauce in a preheated soup tureen; serve immediately.