5 quahog clams or 10 to 12 large cherrystone clams
4 cups water
4 ounces pancetta or lean, cured pork, cut into 1-inch pieces (about ¾ cup)
1 tablespoon good olive oil
1 large onion (about 8 ounces), peeled and cut into 1-inch pieces (1-1/2 cups)
2 teaspoons chopped garlic
1 tablespoon all-purpose flour
2 sprigs fresh thyme
1 pound Yukon Gold potatoes, peeled and cut into ½-inch dice (2-1/4 cups)
1 cup light cream
1 cup milk
¼ teaspoon freshly ground black pepper
Wash the clams well under cold water, and put them in a saucepan with 2 cups of the water. Bring to a boil (this will take about 5 minutes), and boild gently for 10 minutes. Drain off and reserve the cooking liquid, remove the clams from their shells, and cut the clams into 1/2 –inch pieces (1-1/2 cups). Put the clam pieces in a bowl, then carefully pour the cooking liquid into another bowl, leaving behind any sediment or dirt. (You should have about 2-1/2 cups of stock.) Set aside the stock and the clams.
Put the pancetta or pork pieces in a large saucepan, and cover with the remaining 2 cups water. Bring to a boil, and boild for 30 seconds. Drain the pancetta, and wash it in a sieve under cold water. Rinse the saucepan, and return the pancetta to the pan with the oil. Place over medium heat, and cook gently, stirring occasionally, for 7 to 8 minutes. Add the onion and garlic, and continue cooking, stirring, for 1 minute. Add the flour, mix it in well, and cook for 10 seconds. Add the reserved stock and the thyme, and bring to a boil. Then add the potatoes and clams, bring to a boil, cover, reduce the heat to very low, and cook gently for 2 hours.
At serving time, add the cream, milk, and pepper, bring to a boil, and serve. (Note: No salt should be needed because of the clam juice and pancetta, but taste and season to your liking.)