For the stock, season the beef well with salt and pepper. Heat the oil in a large frying pan and brown the meat on all sides. Place the beef in a large saucepan or casserole and cover with cold water (approximately 3 litres/5¼ pints). Bring to the boil then lower the heat and simmer for 1 hour. During cooking, skim off any scum that forms on the top of the stock. Add the onion, bay leaf, peppercorns and coriander seeds and cook for another 30–60 minutes, or until the meat is starting to fall apart and is very tender. Skim any scum from the surface of the stock again.
Remove the bay leaf and peppercorns from the stock with a slotted spoon. Remove the beef from the stock with a slotted spoon, discard the bones and cut the beef into small pieces. Return the beef pieces to the stock.
For the soup, add the chillies, saffron, carrot and rice to the stock in the saucepan and cook for 10 minutes. Add the tomato and pomegranate molasses and cook for another 10 minutes. Season with salt and pepper.
Bash the garlic with a pinch of sea salt flakes using a pestle and mortar. Add the walnuts and pound until it turns into a paste. Add the paste to the soup and cook for another 5 minutes, or until the soup is thick. Garnish with the coriander and basil and serve in warmed bowls with the sourdough bread.