Remove the skin from the onion and cut into cubes. Dissolve the butter (I) and fry the onion in it until translucent. Pour in the soup and the must and then boil the liquid almost to half.
Knead the butter (Ii) with the flour and add to the soup, stirring with a whisk. Season to taste with salt, pepper and a pinch of nutmeg and add the whipped cream.
Now remove the must soup from the stove and add the whisked yolks. The soup must not make any more!
Dice the white bread slices and roast them in butter until golden brown. At the end dust with a little bit of cinnamon.