In a large saucepan, sauté the onions with the butter until the onions are transparent. At this point, you may add 2 to 3 tablespoons of dry white wine (optional) and then add the sliced anise bulbs and lemon juice; stir well. Simmer for 10 minutes. Add potatoes and the stock. Stir well. Cook on low heat for 30-45 minutes. Add salt and pepper to taste. Pour mixture into a blender. Blend until smooth. Pour the mixture back into a pot and heat the soup slowly. Ladle soup into bowls and garnish with fresh anise sprigs and some chopped Italian flat leaf parsley. Makes 2 to 4 servings.