Place the potatoes in a large pot, cover with enough cold water to cover the potatoes by 2 inches (5 cm), and bring to a boil. Season with ½ teaspoon salt, reduce the heat to medium, cover, and cook until the potatoes are fork-tender, 10-15 minutes. Drain and set aside to cool slightly.
In a large skillet over medium-high heat, cook the bacon for five minutes or until crispy. Transfer to a paper towel-lined plate to drain.
Add the onion to the bacon fat in the pan. Cook until tender and golden, about 10 minutes. Remove the pan from the heat.
In a large bowl, whisk together the vinegar and mustard. Season with the remaining teaspoon of salt and the pepper. Add the potatoes, bacon, and onions. Toss to coat. Stir in the chives. Serve warm.