In the dish with a non-stick bottom, melt the butter, add a little oil and fry the finely cut leeks. Soak the peppers briefly in hot water to soften them, then cut them finely.
Add salt, the other spices and about 6 1/5 cups (1.5 liters) of hot water. Boil until ready. Toast the flour in a separate container, taking care not to burn it. When cool, add the eggs and yoghurt and stir well with a whisk. Put this thickening agent back on the stove on low heat and stir until it comes to a boil.
Then, remove it from the fire and add it to the soup while stirring, while boiling on low heat. After 1-2 minutes, the soup is ready.
Season with chopped parsley and serve.