1) Place the potatoes in a medium-size pot and cover them with enough water to extend 5cm above the surface of the potatoes. Salt the water and bring to the boil over medium-high heat. Continue cooking until potatoes are tender when pierced with a fork, about 15 to 20 minutes. Drain and slice into 1/2cm rounds.
2) Cook the bacon in a large skillet over medium-high heat. Once crisp, place on a kitchen towel-lined plate and crumble into small pieces. Pour off the rendered fat, reserving 60ml in the pan.
3) Turn the heat to medium and add the onion. Cook until translucent and just beginning to brown, about 4 to 5 minutes.
4) Whisk in the vinegar, sugar, mustard, and salt and stir until thick and bubbly. Add the sliced, cooked potatoes and toss to coat. Top with the crumbled bacon and garnish with the chives. Serve warm.