Melt butter in a large, deep pot over a medium heat. Add the bacon and cook, stirring until crisp. Remove and let drain on a paper towel placed on a plate.
Cook the onion, carrots, celery leaves and garlic in the butter and fat rendered from the bacon over medium heat. When onion and garlic become translucent, cover the pot and cook all the vegetables until soft, between 5 to 8 minutes.
Uncover the pot and add the flour stirring for approximately 3 minutes. When the flour has become lightly browned, add the broth and tomatoes. Bring the broth to a boil stirring constantly.
Tie the parsley, thyme and bay leaf together with twine and to the pot. Lower the heat to simmer and cook for 30 minutes. When finished simmering, remove the herb bundle and, working with batches, spin the soup in a blender until completely smooth and pureed.
You may pour the soup through a sieve to further puree it at this point, if desired.
When ready to serve, return the soup to the pot and add the crème fraîche or heavy cream, whisking until smooth. Stir in the salt and pepper to taste. Divide the soup into bowls and garnish with the minced bacon. You may also want to add two teaspoons of crème fraîche or a teaspoon of finely chopped parsley as a garnish to each bowl.