Wash all vegetables under running cold water. Leeks and celery need to be washed with special care, as they often carry dirt. Leek: Remove a couple of the outside leaves of leek, and chop off the ends from both sides. Wash and cut on the long side in halves. This way, you can separate the single layers and wash them thoroughly. When it's perfectly clean, chop the leeks roughly.
Cut the courgette in halves and then slice into 0.5cm thick wedges.
Prepare the chicken stock from a stock cube (use real stock if you have one) and set aside, keeping hot.
Peel the onion and cut it into wedges. Peel and finely chop a clove of garlic.
Add the olive oil (you can use also a knob of butter for richer taste) into a stock pot, and set on medium high heat. When hot, add the onion and garlic and fry until soft and glossy.
Add the chopped vegetables and stir. Fry for a couple of minutes and then pour over the chicken stock and cook on medium heat.
After 15 mins, take the soup of the hob, and place on a heat proof mat. Prepare your stick blender and gently blend the soup a few times, until the it becomes thick. You don't want to overdo it, but keep the texture of the vegetables - silky smooth is not what we're looking for here.
When blended just about enough to thicken the soup, place the pot back on hob and bring to boil.
Break the egg into a cup. Stir with a fork until the egg yolk completely mixes with the egg white.
Add the egg mix into the boiling soup, stirring it with the fork - this will create the "ribbon" effect of the egg. Cook for 5 mins and season with salt and black pepper if needed.
Serve with a slice of crispy toast or with a roll and enjoy!