Lamb Soup (kjotsupa)

Place lamb, onion and 2.5 litres water in a large saucepan over medium-high heat and bring to a simmer, skimming impurities from surface. Season with salt and pepper, then reduce heat to low and cook for 1 hour to allow flavours to develop.
Add vegetables, thyme and bay leaves, and cook, topping up with 400 ml extra water if necessary, for a further 1½ hours or until meat is meltingly tender and starting to fall off the bone. Remove lamb from soup and set aside to cool.
Meanwhile, add oats and cook for 15 minutes or until cooked through. Once lamb is cool enough to handle, shred meat from bones, discarding bones, and return to soup. Stir through kale and season.