In a soup pot, bring the wine and 1 1/2 cups of water to a boil. Add the clams, cover and cook over high heat until the clams open, 8 to 10 minutes. Using a slotted spoon, transfer the clams to a bowl; discard any that do not open. Remove the clams from their shells and rinse to remove any sand, then coarsely chop them. Strain the broth into a heatproof bowl, stopping before you reach the sand at the bottom; you should have 3 cups.
Rinse out the pot and dry it. Add the butter and bacon and cook over moderately high heat, stirring occasionally, until the bacon is crisp and golden, about 6 minutes. Add the chopped onion, garlic, celery, thyme and bay leaves and cook until the vegetables are tender, about 5 minutes. Stir in the miso. Gradually add the clam broth. Add the cream and 1 cup of water to the pot and bring to a simmer. Add the potato cubes and season lightly with salt and pepper. Simmer over low heat for about 8 minutes, until the potatoes are tender.
Meanwhile, in a blender, combine the parsley with 1/4 cup of water and puree until finely chopped. Add the oil and puree until smooth. Season with salt.
Using the back of a spoon, crush a few of the potatoes against the side of the pot to thicken the soup slightly. Add the reserved clams and simmer just until heated through. Discard the bay leaves. Serve the soup in bowls, drizzled with the parsley oil.