The best vegetables never find their way onto store shelves. I left some cabbage grow after plucking their heads last fall. This spring, tender shoots of cabbage greens sprouted from their stalks. So green and mild, they make the sweetest of salads. For something to make it onto store shelves, it can’t be too delicate or too delicious, that seems to be the law. Which makes growing them feel illicit, making them taste sweeter still.