Peel, wash and halve the potatoes. Cook in boiling salted water for 15-20 minutes, then drain. In the meantime, peel and wash carrots and cut them into small pieces. Clean and wash the celery, also cut into small pieces. Finely chop some celery green.
Bring the stock to the boil. Season with bay leaf and peppercorns. Cook carrots and celery for about 15 minutes. Meanwhile clean and wash the bell peppers and zucchini and cut them into bite-sized pieces. Peel and finely chop the onion. Wash and chop the thyme. Heat the oil. Fry onion, bell pepper and zucchini for about 5 minutes. Season with salt, pepper and thyme. Deglaze with the vegetables in the broth.
Wash and chop the thyme. Heat the oil. Fry onion, bell pepper and zucchini for about 5 minutes. Season with salt, pepper and thyme. Deglaze with the vegetables in the broth. Add the potatoes. Bring to the boil again briefly and season to taste