Place the potatoes in a large pot and add enough water to cover by 1-2 inches. Bring to a boil. Reduce heat to medium and continue to boil until potatoes are cooked through and can easily be pierced with a fork. Drain and set aside to cool. When cool to touch, peel the potatoes, slice them in half and then slice into 1/4 inch slices. Put the potatoes in a large bowl and carefully add the hot broth and the onions. In a small bowl, whisk together the oil, vinegar, mustard, sugar, salt and pepper until smooth. Gently stir this vinaigrette into the potatoes. Finish with the chives or parsley. Adjust seasoning to taste and serve at room temperature or cold. Kartoffelsalat tastes best if you let it rest for an hour or two to meld the flavors.