01 - If using fresh clams, scrub and rinse thoroughly. Place in a pot with 1 cup water, cover, and steam over medium heat for 5–7 minutes until clams open. Discard unopened clams. Remove clam meat from shells, chop coarsely, and strain reserved cooking liquid through a fine sieve.
02 - In a large pot or Dutch oven, cook the diced bacon over medium heat until crisp. Use a slotted spoon to remove bacon and set aside, leaving the rendered fat in the pot.
03 - Add unsalted butter to the pot. Sauté onion, celery, carrot (if used), and garlic for 5 minutes until softened but not browned.
04 - Sprinkle all-purpose flour over the sautéed vegetables, stirring constantly for 2 minutes to form a roux.
05 - Gradually whisk in clam juice combined with reserved clam liquid. Add diced potatoes, bay leaf, and dried thyme. Bring to a simmer and cook for 12–15 minutes until potatoes are tender.
06 - Stir in whole milk and heavy cream. Add the chopped clams and cooked bacon if desired. Heat gently over low heat for 5 minutes without boiling until warmed through. Season with salt and black pepper to taste.
07 - Remove the bay leaf. Ladle chowder into bowls, garnish with fresh parsley and reserved bacon. Serve with oyster crackers if desired.