Step 1: In a large, heavy-bottomed pot or Dutch oven, cook the diced bacon over medium heat until crispy. Remove the crispy bacon with a slotted spoon and set aside on a paper towel-lined plate for garnish. Leave about 2-3 tablespoons of bacon fat in the pot.
Step 2: Add the diced onion and celery to the bacon fat in the pot. Sauté over medium heat until softened and translucent, about 5-7 minutes. Add minced garlic and cook for another minute until fragrant, being careful not to burn it.
Step 3: Sprinkle the flour over the sautéed vegetables. Cook, stirring constantly, for 1-2 minutes to create a roux. The roux should be pale in color.
Step 4: Gradually whisk in the reserved clam juice and the chicken or vegetable broth. Make sure to whisk constantly to prevent lumps from forming. Bring the mixture to a gentle simmer, stirring occasionally, until it starts to thicken.
Step 5: Add the diced potatoes to the pot. Bring back to a simmer, then reduce the heat to low, cover, and cook for 10-15 minutes, or until the potatoes are tender but not mushy.
Step 6: Pour in the heavy cream and milk. Stir well to combine. Gently heat the chowder until it’s steamy, but do not bring it to a rolling boil after adding the dairy.
Step 7: Add the chopped clams. Cook for just 2-3 minutes, or until the clams are heated through. Overcooking clams will make them rubbery.
Step 8: Season the chowder generously with salt, fresh cracked black pepper, and dried thyme. Taste and adjust seasonings as needed.
Step 9: Ladle the hot clam chowder into bowls. Garnish with the reserved crispy bacon bits and a sprinkle of fresh chopped parsley or chives. Serve immediately with oyster crackers or crusty bread.