This week we decided to try Eddoes, as they have them in Tesco quite often now.
They look like this:
To prepare them you need to boil them for about five mintues then let them cool before peeling them. I leave them on a sheet of kitchen roll as they can go a bit slimy if they don't dry out as they cool. Once peeled you can treat them like potatoes. I tried them roasted first. They roasted a little bit quicker than potatoes, though they don't go quite the same colour as they are more a pure white to start with. They taste quite a lot like potato, but a rather waxy variety, so I decided that they were actually better mashed or boiled. My daughter however thought they were really good roasted.