The Romanesco cauliflower is a freakishly beautiful variety of cauliflower. It’s a lime green color, and each floret is a little spiraling pyramid. It’s said to have been first described by the Italians in the 16th century. They’re all over the place in the markets of Tuscany.
Here’s a good picture and more info.
Cook it as you would any cauliflower. A whole steamed Romanesco makes a beautiful presentation, or you can hack it into bits and roast it. Individual florets make for interesting crudites.