Preheat the oven to 180ºC/350ºF/gas 4. Scrub and trim the carrots, leaving a little of the green tops on. Parboil in a pan of boiling salted water for 5 minutes, then drain and tip into a large roasting tray. Drizzle over 1 tablespoon of oil, season with a pinch of sea salt and black pepper, then toss to coat and roast for 1 hour. Meanwhile, pick the rosemary leaves. Remove the tray from the oven, quickly squeeze over the clementine juice and scatter with the rosemary leaves, then toss together and roast for a final 10 minutes, or until beautifully golden.