Peel the potatoes and cut into cubes. Clean the leek and spring onion and cut into slices / rolls.
Heat the butter in a saucepan on medium heat and sauté the potatoes and vegetables briefly. Pour in the stock and cover the contents of the pot and let simmer gently for about 20 minutes.
Take 2 tablespoons of the vegetables out of the pot and set aside. Turn off the heat, puree the rest of the pot, stir in the sour cream and season with salt, pepper and nutmeg.
Arrange the soup on a plate, add the removed vegetables to the soup, garnish and serve.