Slice the onions very finely and put them in a large saucepan with a few tablespoons of oil, the ham, the bayleaf, the celery, finely chopped, and the thyme, and season with nutmeg, salt and white pepper. When they are a nice golden colour add the white wine. Mix well and add the hot stock. Simmer for 15 minutes.
Put the yolks of 2 eggs in the soup tureen, beat well, add a little vinegar, pour the soup over the beaten eggs, without straining, and add the croûtons of fried bread.