1/2 cup crème fraîche
1 small shallot, minced
2 tablespoons finely chopped dill
2 teaspoons fresh lemon juice, plus more for brushing
Kosher salt and freshly ground pepper
3 baking potatoes (1 1/2 pounds), peeled
4 tablespoons unsalted butter, 2 tablespoons melted
1/4 pound thinly sliced smoked salmon
1/4 pound thinly sliced smoked sturgeon
Extra-virgin olive oil, for brushing
Freshly snipped chives and caviar, for garnish