Preserved lemon, an essential ingredient in Moroccan cooking, is made by pickling lemons in salt, lemon juice, and olive oil. Here, preserving just the peel (begin at least a day ahead) is an easy way to add an exciting note to the crème fraäche.
1/2 cup crème fraäche or sour cream
2 tablespoons olive oil, divided
3 ounces thinly sliced smoked salmon, cut into
1/2-inch-by-2 1/2-inch strips
Using vegetable peeler, remove peel (yellow part only) from lemons. Simmer peel, 1/2 cup water, and 4 teaspoons kosher salt in heavy small saucepan over medium-high heat until salt dissolves. Reduce heat to low and simmer until liquid is reduced to 2 tablespoons and peel is tender, stirring occasionally, about 10 minutes. Transfer peel with liquid to jar. Add lemon juice and extra-virgin olive oil. Refrigerate at least 1 day and up to 1 week.
Drain peel; mince. Stir crème fraäche, minced dill, cilantro, and 1 tablespoon minced peel in small bowl. Cover and chill at least 2 hours and up to 8 hours.
Set rack at lowest position in oven and preheat to 450°F. Brush nonstick baking sheet with 1 tablespoon olive oil. Combine 1 tablespoon olive oil and cumin in large bowl. Add potatoes; toss to coat. Sprinkle with salt and pepper. Arrange potatoes, cut side down, on baking sheet and roast until tender and cut sides are brown, about 12 minutes. Cool slightly.
Arrange potato halves, cut side up, on platter. Top each with 1 teaspoon crème fraäche, 1 salmon strip, and 1/2 teaspoon caviar. Garnish with dill sprigs.
Market tip: Our choice to top the potatoes is American caviar — still indulgent but not endangered.