The gooseberry is the small, plump, translucent berry of a thorny European bush, famous for a mouth-puckering tartness that softens to a honeyed sweet-sour balance as the fruit ripens. Pale green and veined when young, it swells and warms to gold, red, pink or deep purple when mature, and runs through the cool-climate northern kitchen as the soul of summer fools, crumbles, jams and the classic sharp green sauce served against oily mackerel — the partnership that earned it the French name groseille a maquereau, the mackerel currant.