Cook bacon in a large Dutch oven or other heavy pot until crisp. Remove with slotted spoon and set aside, leaving the bacon drippings in the pot.Add onion, carrots, celery, salt and thyme and cook over medium heat until the vegetables soften, about 5 minutes. Add flour, stir and cook another 2 minutes.Add broth and potatoes and bring to a simmer. Cook for about 10 minutes or until potatoes are done.Add chicken and half and half and simmer another 5 minutes. Taste and add salt and pepper as needed. Stir in cooked bacon and scallions and serve.