Melt the butter in a soup pot and sweat the chopped onion, the peeled, sliced carrots and turnips / parsley root and the coriander in it. Season lightly with salt and pepper and cover and let steam over low heat for 20 minutes. Then pour in the broth, bring to the boil and let it steep for 12 minutes. Then strain the soup through a coarse sieve. If it is too thick, add a little more stock, season to taste and finish with the herbs. Serve with white bread cubes fried in butter.