Using a sharp thin boning knife, remove as much meat from the lamb bones as possible. Chop finely and set aside.
Put the bones into a large pot. Roughly chop the carrots, large onion, celery and leek then place in the pot with the garlic and herbs. Cover with at least 4 litres/7 pints cold water. Bring to the boil, season lightly, then simmer gently, uncovered for up to two hours. Skim with a large tablespoon if necessary. Let the liquid simmer down until reduced by nearly two thirds. You need about 1.2 litres/2 pints of lovely sweet stock.
Strain and discard the bones etc. Ideally, cool and chill the stock then you can scrape off any fat that has settled on top.
Place the lamb meat into a large saucepan and cover with cold water. Bring slowly to the boil, skim off any scum, then immediately drain into a colander and rinse in cold running water. This scalding removes fat.
Return the meat to the pan and cover with the stock and bring to the boil. Turn down the heat and simmer partially covered, for about 30 minutes, or until tender.
Meanwhile, peel the carrots and cut into small chunks or shape into neat 'barrels'. Peel the baby onions, it helps to blanch them in boiling water for a minute for easy peeling. Add the small carrots and baby onions to the soup and cook for another five minutes.
Then add the diced potato and cook for another 10-15 minutes, until it starts to dissolve into the soup and thicken it. Finally check the seasoning, adding lots of aromatic black pepper and a little sea salt. Garnish with sliced spring onion and parsley.
