Place the potatoes in a large pot and cover with cold water by at least 1 inch. Season heavily with salt. Bring to a boil over high heat, then reduce the heat to maintain a steady simmer. Cook until the potatoes are easily pierced using a fork, 20 to 25 minutes.

Drain the potatoes and let them cool in a colander.

Meanwhile, in a large skillet over medium heat, cook the bacon, stirring occasionally, until the fat has rendered and the bacon is crisp. Using a slotted spoon, transfer the bacon to a small bowl, leaving the rendered fat in the skillet.

Add the onion to the skillet and cook, stirring occasionally, until softened and translucent, about 5 minutes. Stir in the garlic and cook until fragrant, 1 minute more.

Whisk in the chicken stock, cider vinegar, Dijon mustard, and whole grain mustard. Bring the mixture to a simmer, then remove the skillet from the heat. Taste, and adjust with salt and pepper as needed. If the dressing is too tart, add a little sugar.

Once the potatoes are cool enough to handle, cut them into bite-sized chunks. Add the potatoes to the skillet, season with a generous pinch of salt and pepper, and gently toss to coat in the warm dressing. Let it sit for 10 minutes to absorb the liquid.

Fold the reserved bacon, dill, and parsley into the salad. Serve hot or warm. If the salad appears dry before serving, gently stir in an additional splash of chicken stock.