Cook bacon in a large pot over medium 5-6 minutes until crispy; set aside, leaving drippings.
Melt butter in drippings; cook onion and celery 5 minutes until softened, then garlic 1 more minute.
Sprinkle flour over vegetables; stir constantly 2 minutes to form a roux.
Gradually whisk in clam juice and broth to prevent lumps.
Add potatoes, thyme, bay leaf, salt, and pepper; boil, reduce heat, and simmer 15-20 minutes until potatoes are tender.
Add cream and clams; heat through 5 minutes without boiling.
Discard bay leaf; adjust seasoning and serve hot with crispy bacon and fresh parsley.