Soak the littleneck clams in cold water for 30 minutes so they spit out any sand they may have inside. Drain, and scrub the clams well.
In a large soup pot over high heat, combine the clams and the wine. Cover and cook until the clams open, which should only take 4-5 minutes. If any refuse to open, cook them for a minute or two longer (sometimes they are just stubborn), but if they don’t open after that, throw them away. Remove the clams from the liquid. If the water looks muddy or dark, discard the liquid. Otherwise, you can incorporate it into your soup, but make sure to strain the liquid through a cheesecloth or paper towel-lined sieve to remove any sand that was released.
Clean the pot out and add the bacon. Cook for about 5 minutes over medium heat to crisp up the bacon, then remove the bacon strips from the pan. Add the onion to the bacon fat and cook for 10 minutes until softened, and in the meantime, remove the clam meat from the shells and crumble the bacon.
Add the clam juice and water to the pot, and bring to a boil. Add the potatoes, and reduce the heat to medium low. Simmer the potatoes for 10-15 minutes (uncovered) until almost cooked through. Add the chopped clams, bacon, as well as the cream. Add the pinch of cayenne, and season the liquid to taste with salt and pepper. It’s now ready to enjoy!