Be sure to clean the clams vigorously and thoroughly. Sand and grit is unpleasant even in the best homemade chowder.
4 cups water
24 cherrystone (medium) clams, rinsed well and scrubbed clean
1 tablespoon unsalted butter
1/4 pound slab bacon or salt pork, diced
2 tablespoons finely chopped garlic
2 medium leeks, tops removed, halved, and cleaned, then sliced into half moons
3 medium sweet potatoes, peeled and cut into medium dice
1/2 cup dry white wine (such as Pinot Grigio or Sauvignon Blanc)
3 sprigs of fresh thyme
1 bay leaf
2 cups heavy cream
Freshly cracked black pepper
1/4 cup chopped fresh parsley
Set a large Dutch oven over medium-high heat, pour in the water, and add the clams. Cover and cook until the clams have opened, 10–15 minutes. Note: Discard any clams that fail to open after 15–20 minutes.
Strain the clam broth through a sieve lined with 2 layers of paper towels and set aside. Remove the clam meat from the shells and set aside.
Rinse out the pot, set it on the stove over medium-low heat, and melt the butter. Add the slab bacon or salt pork and cook, stirring occasionally, until the fat has rendered and the pork has started to brown. Remove the pork with a slotted spoon and set aside.
Add the garlic and leeks to the fat and cook, stirring frequently, until the vegetables are soft but not brown, about 10 minutes. Stir in the potatoes and wine and cook until the wine has evaporated and the potatoes have started to soften, about 5 minutes. Add just enough clam broth to cover the potatoes, approximately 3 cups, reserving the rest for another use. Add the thyme and bay leaf. Simmer, partially covered, until the potatoes are tender, about 10 minutes more.
Meanwhile, chop the clams into pieces about the size of the diced pork.
When the potatoes are tender, stir in the cream, chopped clams, and cooked pork. Season with black pepper. Bring the chowder to a simmer and then remove the pot from the heat. Discard the thyme and bay leaf. Allow the chowder to cure for about 10 minutes, reheating it to barely simmering before serving. Portion into deep bowls and garnish with the chopped parsley.