Clean, wash and chop the beans. Peel and wash carrots and potatoes. Cut carrots into slices. Dice potatoes. Peel and finely chop onion. Heat oil in a pot and fry the onion in it. Add the potatoes and steam for 3-4 minutes.
Add carrots and steam for another 2 minutes. Season with salt and pepper. Add stock, bring to the boil and cook over low heat for 10-12 minutes. Wash the thyme, dab dry and chop finely. Add to the soup shortly before the end of the cooking time and season again. Arrange on a plate and sprinkle with parmesan slices and serve