Dice onions and garlic and sauté in a large saucepan in hot butter over medium heat for about 10 minutes while stirring.
Stir in semolina. Pour in the stock and simmer everything in a closed saucepan for about 20 minutes over medium heat.
Whip the cream until it is half stiff. Remove about 6 tablespoon and set aside.
Mix the rest of the cream with the egg yolk and parmesan. Puree the soup with a hand blender, adding the egg yolk and cheese mixture. Season to taste with salt, pepper and nutmeg.
Pour soup into cups and put a dollop of the cream that you have set aside on top. Dust with nutmeg and garnish with chives.