I've enthused before about Cavolo Nero, but this year my crop has excelled.
I planted a whole row; about 20 plants, and we have already enjoyed several pickings.
As a winter 'green' it is almost without comparison. One pulls the leaves as required from the base, and it simply continues to grow. Last year mine continued until about April; in fact I think they were the last plants to be taken out.
The leaves when cooked have a velvety dark flavour, and I imagine are FILLED with goodness. Personally I remove the ribs, and 'steam' in whatever water still clings after washing. They make a perfect accompaniment to a pork chop, a brace of good quality snags, or even a roasted Woodcock (some hope).
As for growing conditions, they like hot, wet, cool, dry, humid, fire, and brimstone; at least that's what's obviously made them grow so well this year.
I recommend the crop to all veg' growers. Cavolo Nero is also known as Black leaf Kale, Tuscan Kale, and Black Cabbage.
Just look at the size of those leaves; and not a single bug in sight. Wonderful.