Peel the carrots and celery and cut into small cubes. Halve the leek lengthways, cut into fine slices and wash.
Heat the oil in a saucepan and fry the celery and diced carrots in it. Deglaze with the vegetable stock. Add the leek. Cook for about ten minutes over medium heat with the saucepan closed.
Add marrowballs and pasta and cook for another eight to ten minutes.
Put the egg and pepper in a cup and mix well with a fork. Pour into the soup while stirring the soup with a fork so that fine threads are formed and the egg does not clump together. Bring to the boil briefly and sprinkle with parsley.
Of course, you can also use other vegetables, such as peppers.