In a large pot over medium heat, cook the chopped bacon until crispy, about 5-6 minutes. Remove bacon and set aside, leaving the drippings in the pot.
Add butter to the bacon drippings. Once melted, add onion and celery, cooking for 5 minutes until softened. Add garlic and cook for 1 more minute.
Sprinkle flour over the vegetables and stir constantly for 2 minutes to create a roux.
Gradually whisk in the clam juice and chicken broth, stirring to prevent lumps from forming.
Add diced potatoes, thyme, bay leaf, salt, and pepper. Bring to a boil, then reduce heat and simmer for 15-20 minutes until potatoes are tender.
Stir in the heavy cream and chopped clams. Heat through for 5 minutes, but do not boil.
Remove bay leaf and taste for seasoning. Serve hot, garnished with crispy bacon and fresh parsley.