Cook bacon in a dutch oven until crisp. Remove to a paper towel lined plate. Don't drain the drippings.
Add the butter to the pan and melt over medium heat.
Add the celery, onion, carrots, garlic, thyme and salt.
Saute for about 10 minutes, stirring frequently to prevent scorching.
Add the chicken stock and bring it to a boil. Cover and reduce heat to simmer.
Simmer for 30 minutes.
Add the milk/cream and remove from the heat to cool slightly.
Puree the soup with either an immersion blender or in a conventional blender (or a Ninja)
Return the soup to the pan to reheat.
If you prefer a thicker soup, add the potato flakes, starting with 1/2 cup.
Chop the bacon and add about 1 tbs to the top of each bowl of soup.
Makes about 7 cups