Place the potatoes in a large pot and cover with water by 1 inch. Season generously with salt. Bring to a boil, then reduce heat and simmer for 15-20 minutes until fork-tender but not falling apart.

While potatoes cook, add the diced beef bacon to a large skillet over medium heat. Fry until the fat renders and the beef is crispy (about 6-8 minutes). Use a slotted spoon to transfer the crispy beef to a plate, leaving the rendered fat in the pan. If the pan is dry, add the beef tallow or oil.

Add the diced onions to the hot fat in the skillet. Sauté for 3-4 minutes until translucent and slightly softened, but not browned.

Whisk in the beef broth, apple cider vinegar, Dijon mustard, and sugar. Bring the mixture to a simmer and cook for 2-3 minutes to emulsify and slightly reduce. Season with black pepper.

Drain the potatoes. While they are still warm, peel them (if desired) and slice into 1/4-inch thick rounds. Place slices into a large mixing bowl.

Pour the hot dressing mixture over the warm potato slices. Gently fold to coat without breaking the potatoes. The warm potatoes will absorb the liquid.

Fold in the crispy beef bacon bits and fresh parsley. Taste and add more salt or vinegar if needed.

Let the salad sit for at least 20 minutes before serving to allow flavors to meld. Serve warm or at room temperature.