Combine stock and sugar in a small saucepan. Bring to the boil over high heat and cook until reduced to a sauce consistency (20-25 minutes).
Meanwhile, heat half the olive oil in an ovenproof frying pan over medium-high heat, add lamb and cook, turning once, until golden (3-4 minutes each side). Transfer to oven and roast until cooked pink (12-14 minutes). Remove from oven, cover with foil and stand to rest (5 minutes), then slice into 4 servings.
Meanwhile, for mashed peas, cook peas in a saucepan of boiling salted water until tender (1-2 minutes). Drain, return to saucepan, add butter, then coarsely mash. Season to taste.
Meanwhile, fry garlic and rosemary in remaining olive oil in a small frying pan over medium heat, stirring continuously until golden (1-2 minutes). Serve lamb rack and mashed peas scattered with rosemary and garlic with sauce drizzled over.
This recipe is from the September 2009 issue of Australian