Preheat oven to 200C. To roast lamb, scatter onion carrot and celery over the base of a large roasting pan. Place lamb seem-side down.
Using a small paring knife make fifteen shallow incisions scattered all over the top of the rolled lamb loin roast; taking care not to cut the kitchen string. Stuff rosemary and garlic into each incision. Drizzle with oil and roast for 1ΒΌ hours or until cooked to you liking. Rest for 15 minutes before carving, to serve.
Meanwhile, cook beans in a saucepan of boiling salted water for 3 minutes or until cooked but still with a crunch. Drain and place in a large bowl with butter. Season to taste.
To serve, Divide beans among four plates and top with carved lamb. Serve with sourdough bread on the side.
Tips
Get you butcher to roll and truss your lamb loin roast for you.
Substitute rosemary with thyme or lemon thyme.
If yellow beans are not in season, substitute with snow peas, sugar snap peas or asparagus.
For a healthier option, get your butcher to trim all the skin from your lamb loin roast.
