Cook the potatoes. Place the scrubbed potatoes in a large pot with 1 teaspoon of kosher salt. Then, add enough water to cover the potatoes by about 1 inch. Bring to a boil over high heat, then reduce to a simmer. Next, cook the potatoes until tender and easily pierced with a fork, about 15-20 minutes. Once tender, drain the potatoes and allow them to cool for about 5 minutes or until you can handle them comfortably.
Cook the bacon. While the potatoes are simmering, heat a large skillet over medium heat. Then, add the bacon slices and cook until browned and lightly crispy, about 5-7 minutes. Next, remove the bacon with a slotted spoon, transferring it to a plate lined with a paper towel. Leave about 2 tablespoons of the bacon fat in the skillet. If less fat has rendered, add a splash of olive oil.
Make the dressing. Add the sliced red onion to the same skillet with the bacon fat. Cook for 2-3 minutes, stirring occasionally, until softened. Then, add the chicken broth, apple cider vinegar, Dijon mustard, whole-grain mustard, honey, and the remaining ½ teaspoon of kosher salt. Whisk until well combined. Bring the mixture to a boil, then reduce the heat and let it simmer for 2-3 minutes until slightly thickened. Stir in the grated garlic and black pepper. The dressing should coat the back of a spoon and leave a trail when stirred.
Assemble the salad. Once the potatoes are cool enough to handle, slice them into ¼-inch thick rounds. Add the sliced potatoes, cooked bacon, and scallions to the skillet with the dressing. Gently toss everything together until the potatoes are well coated. Taste and adjust salt if needed.
Garnish and serve. Transfer it to a serving dish and sprinkle with chopped fresh parsley. Serve warm or at room temperature.