Sauté onion in oil over medium low heat for about 5 minutes. Add brown sugar and continue to cook an additional 5 minutes. Meanwhile, boil potatoes until just tender, approximately 10 minutes. Drain and cool slightly.
Combine the onions, potatoes, chives, and all but 3 Tbsp. of the bacon. Whisk together the mayonnaise, mustard, lemon juice and sour cream. Pour mayonnaise mixture over potatoes. Toss together. Sprinkle with remaining fried bacon. Garnish with reserved chives.