Heat the flour gently over medium heat until it begins to turn pale golden brown, stirring constantly. Remove from heat.
n another pan, saute onions in butter. When transparent, blend them into the flour. Gradually add the beef stock, the wine and the salt and pepper to taste. Cook gently, stirring frequently, for about 30 minutes.
Put a slice of bread in each person's bowl with a good sprinkling of cheese on top. Pour soup into each bowl and serve at once.