Cook the whole unpeeled garlic bulb in a preheated oven at 200 ° C on the middle rack for 30 minutes (convection 25 minutes).
Cut the onions into fine cubes and sauté them in a saucepan with butter or margarine, then pour in the meat stock and simmer on a low heat for about 20 minutes, covered. Meanwhile, peel the cloves of the slightly cooled garlic bulb. Add the garlic to the soup and puree with the magic wand. Add the cream and bring to the boil briefly.
Season the soup with salt, pepper and the white wine vinegar. Whisk the 2 egg yolks in a cup with a little soup and beat with a whisk under the almost boiling soup. Remove the soup from the hob, serve and sprinkle with coarsely grated Parmesan and the chopped chives.
Toasted white bread or toast bread goes well with it.