Place potatoes in a large saucepan. Cover with cold water and salt lightly. Bring to a boil over high heat. Reduce heat to medium and simmer for 45 to 50 minutes or until fork tender. Drain and allow to cool slightly.
Meanwhile, heat oven to 450°. Place salmon in a baking dish skin-side down and season with 1/8 teaspoon each of the salt and pepper. Bake at 450° for 20 minutes.
Peel potatoes, slice into 1/2-inch slices and place in large bowl. Stir in onion. In a small bowl, whisk together mayonnaise, vinegar, dill, remaining 1/2 teaspoon salt, remaining 1/4 teaspoon pepper and the nutmeg. Gently stir into potatoes. Remove skin from salmon and flake with a fork. Fold into the potatoes.
Cover and refrigerate for at least 2 hours.