Place potatoes in a large saucepan and cover with water. Bring to a boil. Reduce heat; cover and simmer until tender, 15-20 minutes. Meanwhile, in a small bowl, combine the cream cheese, sour cream, dill, lemon zest, capers, salt and pepper.
Drain potatoes; cut in half. Cut a thin slice from the bottom of each potato half to level if necessary.
Dollop cheese mixture onto potatoes, 2 teaspoons on each. Top with salmon. Garnish with dill sprigs if desired. Chill until serving.