1.2 kg unpeeled baby red potatoes (no larger than 2-inches in diameter)
1 tbsp plus 1/2 tsp kosher salt, divided
4 slices thick-cut bacon (180g), diced
1 small yellow onion, diced
1 to 3 tbsp vegetable oil
3 tbsp white wine vinegar
1 tbsp granulated sugar
1 tbsp whole grain mustard
1/2 tsp freshly ground black pepper
2 tbsp chopped fresh chives
1 tbsp chopped fresh flat-leaf parsley leaves
Place the potatoes and 1 tablespoon of the salt in a large saucepan. Cover by 1 inch with cool water, then bring to a boil over high heat. Reduce the heat to medium and simmer until the potatoes are easily pierced with a knife, 30 to 35 minutes. Meanwhile, cook the bacon.
Place the bacon in a large skillet over medium heat and cook until the fat begins to render, about 8 minutes. Add the onion and cook until the onion and bacon brown and the bacon is crisp, 13 to 15 minutes. Use a slotted spoon to transfer the bacon and onions to a paper towel-lined plate. Measure the remaining fat in the pan. If there is less than 3 tablespoons, add enough oil to equal 3 tablespoons.
Drain the cooked potatoes in a colander and rinse under cold water just until they are cool enough to handle. If desired, peel potatoes with your fingers or a vegetable peeler. Slice into 1/4-inch thick rounds and transfer to a large bowl.
Place the vinegar, sugar, mustard, pepper, remaining 1/2 teaspoon salt, and the bacon fat in a jar, cover, and shake to combine. Add the chives, parsley, bacon and onion mixture, and dressing to the sliced potatoes, toss, and set aside for 10 minutes. Serve warm or at room temperature.