1. Scrub the clams well to remove any mud. Use a small sturdy knife to open, working over a bowl to save the juices. Discard the black neck skin and if they are too large to eat in a bite, cut into smaller pieces. Or steam the clams in about ½ cup water just until they begin to open, 5 to 8 minutes. Shuck, discarding the neck skin and cutting up if large. Reserve the broth, letting any sediment settle to the bottom of the pot.

2. In a large soup pot, cook the bacon over medium heat until crisp, about 10 minutes. Remove with a slotted spoon and reserve, leaving the bacon fat in the pot. Add the onion and cook until it begins to soften, about 5 minutes. Add the potatoes and enough water or a combination of water and clam broth to cover. Bring to a simmer, reduce the heat to medium-low, and cook until the potatoes are tender, about 15 minutes. Add the milk, evaporated milk, butter, and clams with any juices. Simmer over low heat until the butter melts and the clams are cooked, about 5 minutes. Add the reserved bacon (or sprinkle the bacon on top just before serving) and parsley and season with salt and pepper to taste. Serve immediately or cool and refrigerate overnight. Reheat gently.