01 - Slice the tops off sourdough boules and hollow out centers, leaving a 1-inch thick shell; set aside.
02 - In a large pot or Dutch oven over medium heat, cook diced bacon until crisp. Remove with a slotted spoon and set aside.
03 - Add butter to the pot; sauté onion, celery, carrots, and garlic until softened, approximately 5 minutes.
04 - Sprinkle flour into the vegetable mixture and cook, stirring constantly, for 2 minutes to form a roux.
05 - Gradually whisk in reserved clam juice and bottled clam juice until the mixture is smooth.
06 - Add diced potatoes, dried thyme, bay leaf, salt, and black pepper. Bring to a simmer and cook until potatoes are tender, about 15 minutes.
07 - Stir in chopped clams, cooked bacon, whole milk, and heavy cream. Simmer gently for 5 minutes without boiling. Remove bay leaf.
08 - Adjust seasoning to taste and stir in chopped parsley.
09 - Ladle the hot chowder into prepared sourdough bowls and serve immediately.