Ingredients

3 to 4 pounds littleneck clams (about 32), scrubbed

2 sprigs thyme, plus leaves for serving

2 tablespoons unsalted butter

2 medium leeks, white and light-green parts only, halved lengthwise, thinly sliced, washed well, and drained

1/4 cup dry vermouth

3 stalks celery, cut into 1/2-inch pieces

1 pound Yukon Gold potatoes, peeled and cut into 3/4-inch pieces

1 cup heavy cream

8 ounces hot-smoked salmon (available at specialty stores and some supermarkets), skin removed, cut into 1-inch pieces

Freshly ground pepper

Preparation

Bring clams, thyme sprigs, and 4 cups water to a simmer in a large pot. Cover; cook until clams open, 5 to 10 minutes. Transfer to a bowl, discarding any that remain closed. Strain liquid into a bowl. Reserve 12 clams; coarsely chop meat from remaining ones.

Melt butter in pot over medium. Add leeks; cook, stirring occasionally, until soft, 5 minutes. Stir in vermouth; cook until almost evaporated, 2 minutes. Add celery, potatoes, and clam liquid. Simmer, partially covered, until potatoes are tender, 15 to 20 minutes; mash a few with the back of a spoon to thicken soup. Stir in cream, salmon, and all clams. Cook until heated through, 1 minute. Season with pepper and serve, topped with thyme leaves.