New England Clam Chowder

Name: New England Clam Chowder
Ingredients: 6 sprigs fresh thyme; 2 bay leaves; 2 pounds potatoes, peeled and cut into 1/2-inch cubes (about 5 cups); 2 cups heavy cream; 1/2 teaspoon freshly ground black pepper; 1 1/4 teaspoons salt, or to taste; 6 tablespoons cold unsalted butter, cut into half-tablespoon pieces; 1/4 cup finely chopped fresh parsley; 1/4 cup finely chopped fresh chives or green onions; 10 pounds small quahogs or large cherrystone clams, scrubbed and rinsed, open clams discarded; 6 slices bacon, cut crosswise into 1/2-inch strips; 4 tablespoons unsalted butter; 2 medium leeks, white and light green parts only, halved lengthwise and thinly sliced crosswise (2 1/2 to 3 cups); 1 cup finely chopped onions; 1 cup finely chopped celery; 2 teaspoons minced garlic