Catalan Soup

Slice the onions thinly and brown gently in a saucepan in a little olive oil. Quarter the tomatoes and chop the celery. Add them, with the ham, to the pan. Cook for a few minutes before adding the wine. Simmer gently for a few minutes. Cut the potatoes into small pieces and add to the pan with the thyme, nutmeg and stock. Simmer gently for 30 minutes. Just before serving, beat the egg yolks together with a little of the soup. Stir well into the rest of the soup. Sprinkle with chopped parsley.