Put the potatoes in a 4- to 5-quart saucepan and cover by about 2 inches with cold water. Add 1 Tbs. salt and bring to a boil over medium-high heat. Boil gently until the potatoes are tender enough to pierce easily with a skewer, about 20 minutes. Don’t overcook them or they will fall apart.
Meanwhile, put the bacon slices in a cold 10-inch skillet and cook over medium heat, turning occasionally, until crisp, about 10 minutes. Transfer to a paper-towel-lined plate, reserving the drippings. Coarsely chop or crumble the bacon and set aside. In a medium mixing bowl, combine the shallot, vinegar, lemon juice, lemon zest, sugar, and 1/2 tsp. salt.
Drain the potatoes in a large colander and let them cool slightly. When the potatoes are cool enough to handle, cut in half any that are larger than a walnut. Taste a bit of potato skin: If it’s bitter or feels tough, peel all the potatoes with a paring knife.
Drop the potatoes into the bowl with the shallot mixture. Add the olive oil, 2 Tbs. of the chives, 1 Tbs. bacon drippings, and the chopped bacon. Toss to combine. (It may appear that there’s too much dressing, but it will be absorbed.) Let the salad sit for 20 minutes. Season to taste with black pepper and more salt, if necessary. Sprinkle with the remaining 1 Tbs. chives. Serve warm or at room temperature.