Put the nettle leaves in a saucepan twice the size of the amount of water used.
Add pepper and salt and bring to the boil briefly.
Remove the saucepan from the heat and finely puree the leaves with a blender.
Add the butter and the crumbled bouillon cube and continue cooking at a low temperature.
Chop the scallions (bulb and green tops) and add them.
While the soup is simmering, mix the cornflour with the cold milk and the whipped cream and add to the soup.
Continue to cook, stirring constantly, at the lowest possible temperature until the soup has thickened.
Season with nutmeg and serve the soup.