Wrap the garlic bulbs in foil and bake in the oven for 30 minutes then remove and leave to cool a little. Melt the butter in a heavy based saucepan and gently cook the onion and leek for 3-4 minutes with a lid on until soft. Remove the foil from the garlic, half the bulbs and squeeze out the pulp into the pan with the onion and leek. Add the flour to the pan and mix well then gradually stir in the vegetable stock, season and simmer for 40 minutes then remove from the heat and blend in a liquidiser until smooth and strain through a sieve into a clean pan.
Meanwhile break the sourdough slices into rough croutons and toast under the grill until lightly coloured. Re-heat the soup, add the parsley and cream and re season if necessary. Poach the eggs, ladle the soup into warmed serving bowls, drop an egg into each bowl and scatter over the croutons.