Add the chopped pancetta to the large pot. Raise the heat to medium and fry the pancetta until golden brown, about 8 minutes. Remove the pancetta from the pan and set aside.
Stir the celery and onions into the oil from the pancetta. Saute until the celery and onions are soft, about 5-6 minutes. Stir in the garlic and saute for 1-2 more minutes.
Stir in the flour and combine well with the vegetables. Add ½ cup white wine and bring to a simmer. Deglaze the bottom of the pan, using a wooden spoon to scrape up the brown bits. Then add the chicken stock, 2 cups of stock from the clams, thyme, and a parmesan rind, and bring the soup to a boil.
Add the potatoes once the soup comes to a boil. Lower the heat to a simmer and simmer for 20 minutes or until the potatoes are fork-tender.
Use an immersion blender to gently blend the soup for about 5-10 seconds. You just want to break up the potatoes slightly, but not completely. Add 1 can of white clam sauce and the chopped clams. Simmer for 2-3 minutes.
Remove the thyme and parmesan rind. Stir in the heavy cream. Serve with oyster crackers and chopped chives.
Steaming clams
Scrub and rinse the clams.
In a medium pot, add 1 cup of water, ½ cup of white wine, and juice from a lemon over medium-high heat. Add the clams to the pot and steam until they open. Remove the clams as they begin to open and set them aside.
Strain the liquid from the pot into a measuring cup and save it for the soup. You need to strain it through a small mesh strainer so that it can remove any sediment from the clams, especially if they're wild-caught.
Notes
Always fry pancetta starting from a cold pan. This will let the fat begin to render first so that the meat in the pancetta doesn't burn.
Use russet potatoes in clam chowder because they're starchy and will naturally make the soup creamy.
Salt is necessary in any recipe, but in a soup like this with multiple salty flavors like pancetta and briny clams, be careful with adding extra salt or using store-bought chicken broth.
Don't add the clams until the last few minutes of cooking the soup. They will get rubbery if you simmer them for 20 minutes.