Remove the tough part from the asparagus, once rinsed chop them into bits. Peel the carrots, rinse them and chop them into strips and blanch them for 3-4 minutes in boiling water. Clean the celery, rinse it and chop it into strips then blanch it in boiling water.Chop the onion finely and fry it until soft in a pan over a medium heat with a dash of oil and a knob of butter. Add the carrots, the celery, the asparagus, a pinch of salt and pepper, cover the pan and simmer for 7-8 minutes. In the meanwhile cook the pasta in a large with plenty of boiling water, drain it al dente and mix it with the vegetable sauce. Serve immediately.