Preheat oven to 220C. For tarragon butter, process ingredients in a food processor until smooth, season to taste and set aside.
Place chicken on an oven tray lined with baking paper, pat dry with paper towels, then spread skin thickly with tarragon butter (it’s easiest to do this with your hands). Roast chicken, basting occasionally with pan juices, until golden brown and juices run clear when the thigh is pierced with a skewer (20-25 minutes). Place on a platter and squeeze lemon juice over.
Meanwhile, line a roasting pan with baking paper. Add carrots and toss with oil, thyme and lemon rind in pan, season to taste and roast until tender and golden brown (15-20 minutes). Add to platter, drizzle roast chicken with pan juices and serve with green salad.