Heat oven to Gas Mark 3, 170°C, fan 150°C. Crush garlic in their skins and place them with the rosemary sprigs in a roasting pan. Put the lamb on top, add water and cover tightly with nonstick baking parchment. Bake in the oven for 4 hours.
Trim and peel carrots and swede then slice very thinly (a mandolin is best). Lightly butter a shallow ovenproof dish and place a layer of carrot followed by swede, then repeat, sprinkling thyme leaves in between each layer.
Pour over vegetable stock, brush top with melted butter, press down and cover with nonstick baking paper. Place in lower part of the oven and bake for 2 hours.
In a large pan place 4 tablespoons of water, add cabbage and cook a few minutes on high. Add sesame oil and seeds, mix well. Cook for 5 minutes, turning all the time to ensure even cooking.
When lamb is cooked, remove excess fat from top of juices and discard. Carve meat and serve with the vegetables, topped with pan juices from lamb.
For top tips on protecting you and your family when preparing raw meat and poultry, visit Food Safety in the Home and view the full Food safety at home video.