Tuscan kale (cavolo nero) has long, blistered, very dark green leaves. It is the soul of ribollita and becomes sweeter after the first frosts.
Separate the leaf from the tougher rib, which can be chopped and cooked separately. The leaves, cut into strips, can be sautéed, cooked with rice or in barley risotto; baked with a drizzle of oil they become crunchy chips.