1. Peel the potatoes and chop them into bite-size pieces, you should have 4 cups. Make sure the celery and onion are minced into very fine pieces about the size of a grain of rice. The carrot should be grated into very small pieces, not shredded.

2. Combine the vegetables with the chicken stock, salt, and vinegar in a large sauce pan over medium heat. Bring the stock to a boil, then turn down the heat, cover the pan, and simmer for 20 minutes.

3. wisk together the flour and milk in a medium bowl.

4. Remove the saucepan of vegetables from the heat and add the flour and milk mixture. Put the pan back on the heat and simmer, uncovered, for 5 to 8 minutes or until the soup has thickened.

5. Add 1 cup of cheddar cheese to the soup and simmer until melted. By this time the potatoes should be tender and fallling apart. If not , continue to cook until the soup is as thick as you like it.

6. To serve, spoon the soup into bowls. Divide the remaining 1 tablespoon of cheddar and the montery jack and sprinkle on the soup. Crumble the bacon and sprinkle it evenly onb top of the cheese. Top off each bowl of soup with chopped green onion.