Boil the chicken, debone it and tear it into medium-sized pieces. Pour the desired amount of water in a pot, then add the meat, pour the broth in right after.
Add the finely diced onions, potatoes and carrots (optional). Leave to boil until the potatoes and carrots are cooked. Once they are, add in a little oil (optional), salt, ground black pepper and the vermicelli. Once the vermicelli boils a bit, take the soup off the stove and let it cool a little.
To make the thickening agent, stir 2 tbsp yoghurt with 1 egg and 2 tbsp flour in a bowl. You have to stir well, so there's no lumps.
Next, scoop a little of the soup and add it to the thickening agent mixture in a thin trickle, while stirring nonstop.
Pour the thickening agent back into the soup in a thin trickle, while stirring nonstop, so it doesn't curdle. Finally, serve.