*If using fresh clams: Place the clams and 4 cups water in a stock pot and bring it to a boil. Cook just until the clams have opened, about 8-10 minutes. After 10 minutes, discard any unopened clams. Use a slotted spoon to remove the cooked clams, let them cool, then remove the meat and roughly chop it. Set aside. *If using canned clams, save them until step 5.
Fry the pancetta in a medium stock pot until crispy then remove with a slotted spoon, leaving about a tablespoon of the grease in the pot.
Add the butter to the pot along with the onions, celery and garlic. Cook over medium-high heat for 6-8 minutes until softened but not browned. Add the flour, stir to combine and cook for a minute.
Add the broth and white wine, stirring to prevent the flour from clumping, and bring to a simmer, stirring constantly. Add the potatoes, thyme, bay leaves, salt, pepper and half of the pancetta. Simmer the chowder for 20-25 minutes until the potatoes are extremely tender. The consistency is right when the potatoes are so soft that some have begun to fall apart. If you prefer the chowder to be thicker or less chunky, discard the bay leaves and use an immersion blender (or transfer 1 cup of the chowder to a blender) puree just a small portion of it.
Add the clams, cream and parsley and heat through for 5 minutes, add salt and pepper to taste, and serve immediately sprinkled with the remaining pancetta, fresh parsley and oyster crackers.