Take a head of broccoli, tint it lime green and decorate it with spires and minarets and you've got Romanesco. So distinctive-looking is the Romanesco that its structure has been studied by avant-garde architects for new models of buildings (it's sometimes called fractal broccoli). Actually, Romanesco isn't really a broccoli at all. It's a cauliflower. The confusion is understandable -- the two families have been crossbred for so many centuries that they are largely indistinguishable.
Recent DNA testing has revealed Romanesco's true heritage, but someone could have just asked a cook -- Romanesco definitely tastes like cauliflower and benefits from the same preparations. Cook it briefly to emphasize the grassy, vegetal aspects of its flavor; cook it longer and a subtle, earthy sweetness emerges.
How to choose: Whatever its lineage, select Romanesco as you would broccoli or cauliflower -- you want firm heads that are heavy for their weight and show no signs of discoloration or sunburn.
How to store: Refrigerate Romanesco in a tightly sealed bag.
How to prepare: One great simple dish is to steam Romanesco, then break it into florets (this way it stays a little crisp). Dress it with a vinaigrette made with good olive oil, red wine vinegar, minced garlic and chopped pitted black olives.