Melt the butter in a Dutch oven set over medium heat. Add the bacon and fry until golden and crisp, 6-8 minutes; remove about half to a plate lined with paper towels and cover with aluminum foil.
Add the onion, celery, garlic, potatoes, and a pinch of salt to the Dutch oven, sweating until starting to color, about 10 minutes.
Whisk in the cornstarch and cook for 2 minutes; whisk in the milk followed by the stock in a slow, steady stream until fully incorporated.
Add the bay leaves and bring the mixture to a simmer, cooking steadily until the potatoes are very soft, 15-20 minutes.
Discard the bay leaves. Working in batches to best fit your blender, transfer the contents of the Dutch oven to a food processor or blender and purée until smooth, scraping down the sides of the processor as needed.
Pour back into the Dutch oven and whisk in the cream. Bring the chowder to a simmer and season to taste with salt and pepper; keep warm over very low heat.
Place the clams in a large saucepan set over high heat. Add the wine, cover the pan with a lid, and cook until the clams have steamed open, 3-4 minutes; discard any that don't open.
Drain the clams and leave to cool for 3 minutes. Pick the meat from about half the shells; stir the picked clam meat into the chowder along with the clams in their shells, parsley, and reserved bacon.
Serve straight away for best results.
