Preparation Bring a large pot of heavily salted water to a boil over high heat. Working in batches, blanch the cavolo nero in the rapidly boiling water for 2 minutes. Drain, let cool, and squeeze out excess water with your hands. Coarsely chop and set aside. Heat a large pot or Dutch oven over medium heat for 2 minutes. Pour in 1/4 cup oil, and add the rosemary sprig and the chile. Let them sizzle in the oil for about a minute. Turn the heat down to medium-low, and add the sliced onion. Season with 1/2 teaspoon salt and a pinch of freshly ground black pepper. Cook for 2 minutes, stirring often, and stir in the sliced garlic. Continue cooking for another 5 to 7 minutes, stirring often with a wooden spoon, until onion is soft and starting to color. Add the cavolo nero and the remaining 2 tablespoons oil, stirring to coat the greens with the oil and onion. Season with a heaping 1/4 teaspoon salt, and cook the greens slowly over low heat for about 30 minutes, stirring often, until they turn a dark, almost black color and get slightly crispy on the edges. Remove chile before serving.