In large pot, combine potatoes with enough cold water to cover by 1 inch. Add 1 teaspoon salt. Simmer 30 minutes or until fork-tender.
In skillet, heat 2 tablespoons oil. Add leek, shallots, garlic; sauté 3 minutes to slightly soften. Set aside.
Drain potatoes. Slice and transfer to a large bowl. Add leek mixture; toss to combine. Cover to keep warm.
In bowl, whisk vinegar, mustard, remaining salt, pepper. Whisk in 1/3 cup oil. Add with parsley to potatoes.
Heat grill pan or nonstick skillet. Add sausage; cook 6 minutes on each side or until internal temperature reaches 160 degrees F on instant-read meat thermometer. Let stand 2 minutes.
Slice sausage on diagonal. Use to garnish warm potato salad. Makes 6 servings.