Thoroughly wash the leaves, then chop them in long strings, like large noodles.
Bring the broth (stock) to boil, add the leaves and let simmer for a couple minutes.
Set the broth with the leaves aside on the stove top to cool off for about 5 minutes.
In a small pot, pour 2-3 ladles of the hot broth - without any of the leaves - and let it cool off for another minute.
Mix the yolk with the créme fraîche, in a small cup.
Slowly incorporate the yolk and créme fraîche mix into the broth that you set aside in the small pot, whisking carefully so the yolk will not coagulate.
Pour the newly obtained mix into the pot with the broth and the leaves and mix well.
Serve hot immediately, or fridge chilled. Do not reheat!
Tip: Try adding orache and lovage leaves for extra flavour and nutrients!