[Brassica oleracea Group Botrytis ??]
This is probably pretty much what European cauliflower looked like in the time of the Roman Empire. Selective breeding during Medieval and Renaissance times developed the heavy white curd cauliflower we enjoy today.
The taste of this vegetable is very much that of cauliflower, but significantly more assertive than our regular white cauliflower - less of a blank canvas and more of a feature flavor. Raw, it is a little bitter, but not objectionably so, and the bitterness fades with cooking. The photo specimen was a head 8 inches across and weighing 14-1/4 ounces
More on Cabbage Flowers.
Buying: This vegetable is not at all easy to find. I first saw it in a large Asian market in Los Angeles (Alhambra) in mid July 2017. It was sold for 2017 US $1.98 / pound. Note that the curds at the ends of the stems will never be pure white like regular cauliflower, but will have a greenish yellow color.
Storage: If it is in good condition, it will hold for 4 or 5 days refrigerated loosely wrapped in plastic.
Cooking: This vegetable can be used raw in salads, but is more often cooked. Steaming and stir frying are suitable methods. Do not overcook, the green stems should still have a little crunchiness to them.