Rub the garlic around a pan. Heat the butter in the same pan, add the flour and cook over a medium heat while stirring with a whisk; the flour must not take on any colour. Remove the pan from the heat, pour in the stock and wine at once, bring to the boil, stirring continuously. Reduce the heat, simmer for approx. 10 mins., stirring occasionally. Combine the cream and egg yolk in a bowl. While stirring, add 3 tbsp of hot soup, then pour slowly back into the pan, stirring continuously. Heat the soup again gently, season.
Serve the soup, scatter the air-dried ham and chives over the top.