Place the racks of lamb in a glass or ceramic dish.
Scatter garlic and rosemary over the lamb, then drizzle with olive oil.
Marinate for at least 4 hours or overnight, turning occasionally.
Preheat oven to 200°C fan (220°C conventional).
Season lamb generously with salt and pepper.
Heat a heavy pan over medium-high heat and sear the lamb on all sides until browned.
Arrange racks in a roasting tin with bones interlinked.
Roast the Roast Rack of Lamb with Rosemary:
15 minutes for rare
20 minutes for medium-rare
25–30 minutes for well done
Test doneness using a skewer or thermometer.
Rest the lamb for 10 minutes under foil before carving.
Slice into cutlets and serve warm.