Heat the oil and saute the onions, garlic, leeks and fennel for a few minutes. Add the potatoes, stock, cinnamon stick, lemon peel, allspice and bay leaves.
Bring to the boil, then gently simmer for 20 minutes. Remove the cinnamon, lemon and bay, and season. In a separate bowl, whisk the egg yolks and cream, then stir in a large spoonful of soup.
Whisk well, then tip into the soup. Slowly return the soup to just below boiling, stirring. Remove from the heat and adjust the seasoning with salt, pepper and lemon juice. Drizzle each bowl with oil and sprinkle with cinnamon and parsley.