Preheat oven to 375 degrees.
Put potatoes in large pot and cover with cold water. Bring water to rapid boil over high heat and cook for 10 minutes, until just fork-tender. Drain.
Place a large rimmed baking sheet in oven to get nice and toasty. Toss the potatoes in 2 tablespoons olive oil (or if using duck fat, add it to baking sheet to melt in oven, then toss with potatoes). Season potatoes with 1/2 teaspoon sea salt and roast for 40 to 45 minutes, giving the pan a shake halfway through, until skin is golden and crispy and the flesh is tender.
While potatoes roast, in a large bowl, whisk together tahini, lemon juice, honey, Dijon, garlic and 3 tablespoons water. Whisking continuously, add 1/4 cup olive oil in slow, steady stream until vinaigrette is thick, creamy and emulsified. Season with remaining 1/4 teaspoon sea salt.
Toss finished potatoes in vinaigrette and set them on serving platter. Arrange salmon on top and spoon on the sour cream. Sprinkle dill over all and garnish with parsley. Serve warm. (If you don't plan on serving salad right away, of if you're a fan of cold potato salad, wait to add the smoked salmon, sour cream and dill until just before serving.)