4 dozen hard-shell clams, scrubbed, or 1 quart shucked cooked clams with their broth
1/4 pound cubed salt pork or 6 slices bacon
1 onion, coarsely chopped
6 medium potatoes, peeled and cut into 1/2-inch cubes
2 cups milk
2 cups half-and-half or evaporated milk
6 tablespoons (3/4 stick) unsalted butter
freshly ground pepper
Pour clams into a large pot with 1 cup water. Cover, bring to a boil, and cook until shells open, about 10 minutes. Allow to cool, then shuck clams and set aside. Pour off broth and reserve, taking care not to disturb any sediment in the bottom of the pan.
Cook salt pork in a large saucepan over medium heat until the fat runs. Add onion and cook, stirring, until tender. Pour off half the fat.
Add potatoes to the pan and stir well. Add clam broth and just enough water to cover the potatoes. Simmer until potatoes are tender.
Add milk and half-and-half (or evaporated milk); bring to a simmer. Add clams and butter; simmer a few minutes until clams are heated through and butter is melted. (Do not boil or clams will be tough.) Season with salt and pepper.