Cut carrots into slices, leek into rings and celery into small cubes. Peel and dice the potatoes as well.
Heat oil in a pot. Sauté vegetables and potatoes in it. Deglaze with vegetable stock and simmer for 20 minutes.
Finely chop the parsley. Cut the wiener into slices.
Remove some of the vegetables and puree the rest of the soup. Add the vegetable pieces to the soup, season with salt and pepper. Refine the soup with parsley.