if you have Stephanie's cooks companion - I use her instructions, she explains it better than I do
peel the stalk - take off outer leaves and chop the top off - so you just get the soft yummy bits - you can see from the photo how I just chop off the tops - we find the smaller ones yummier.
and they are really bitter before cooking so your hands and everything they touch go bitter too - then they go really sweet - odd but true
put straight away into lemoned water - to stop them going yellow
boil them in salted water - I put them in when the water is boiling but we have done it both ways and it works - and boil for 15 minutes or until soft - weighed down with either a plate or a smaller than the pot lid - this is as they float and then wont cook properly