Heat 8 1/3 cups (2 L) water in a pot, add the chicken meat, 1/2 tsp salt and boil 45 min. If the chicken meat is from a free-range chicken, it will take longer to boil until cooked - about 60 min.
Once cooked, remove the foam that's formed on top, take the meat out and strain the broth. Return the broth to the pot and put the diced carrots and tomato, plus the grated onions in it.
Let them boil for 10 min., then add the crumbled vermicelli, celery and a little oil if needed. Cut the meat into tiny pieces and add it to the soup.
Season with turmeric and black pepper. Boil another 10 min. and remove from the stove.
Beat the egg with the yoghurt in a bowl to make the thickening agent. Pour a little of the hot broth into it in a thin trickle.
Stir nonstop while pouring in the broth to prevent the thickening agent from curdling. Then, while stirring nonstop again, pour the thickening agent in a thin trickle into the soup. Sprinkle with chopped parsley.