Place whole potatoes in a large pot with cold salted water and bring to a boil.
Cook until potatoes are fork-tender but still hold their shape.
Drain the potatoes well and allow them to steam dry for a few minutes.
Peel the potatoes once cool enough to handle and slice them into uniform rounds.
In a saucepan, heat the vegetable oil over medium heat and sauté the diced onion until translucent.
Whisk in the vegetable broth, apple cider vinegar, and Dijon mustard until well combined and simmering.
Pour the warm dressing over the sliced potatoes and toss gently to coat evenly.
Season generously with salt and fresh cracked black pepper.
Garnish with fresh chopped parsley before serving warm or at room temperature.