1) Heat the butter in a large soup pot over medium-high heat. Add the bacon and cook, stirring, until crisp and most of the fat has rendered, about one minute. Using a slotted spoon, transfer the bacon to a kitchen towel-lined plate and set aside. Lower the heat to medium, add the onion, carrots, celery, and garlic and cook, covered, stirring occasionally, until soft and fragrant, about 8 minutes.
2) Stir in the flour and cook, stirring, for three minutes. Pour in the stock and crush the tomatoes through your fingers into the pan. Bring to a boil while whisking constantly.
3) Tie the parsley sprigs, thyme, and bay leaf together with a piece of kitchen string and add to the pot. Lower the heat and simmer for 20 minutes. Remove from the heat and let cool.
4) Remove and discard the herb bundle. Working in batches, transfer the mixture to a blender and puree until smooth. Return the puree to the pot and reheat over medium heat.
5) Whisk in the double cream, salt, and pepper, to taste. Divide among warm soup bowls and serve immediately.