In a large pot, cook the bacon over medium heat until crispy (if using). Remove the bacon and set it aside, leaving the drippings in the pot.
Add butter to the pot with the bacon drippings. Once melted, add the chopped onion and celery. Sauté for about 5 minutes, until the onions are translucent.
Sprinkle the flour over the sautéed vegetables, stirring constantly for about 2 minutes to create a roux.
Gradually add the clam juice and bring the mixture to a boil, stirring to avoid lumps.
Once boiling, add the diced potatoes and thyme. Reduce to a simmer and cook for approximately 15 minutes or until the potatoes are tender.
Stir in the reserved clam juice, diced clams, and heavy cream. Allow it to heat through for another 5 minutes. Season with salt and pepper to taste.
If using, add the crisped bacon back into the chowder and stir well.
Remove from heat and let sit for a few minutes to thicken up.
Notes
Serve in warm bowls, garnished with fresh parsley and black pepper. Pair with oyster crackers or soft bread.