Wash and roast the potatoes at 375°F until just tender (~1 hour)
Slice bacon into ~1⁄2″ strips
Dice the yellow onion
Chop the parsley
Make the dressing
Put the bacon in a medium stick skillet
Cook on medium until crisp and you get bacon foam
Add the onion and cook until they turn translucent and soft
In parallel
Cut potatoes into half lengthwise,
then into half lengthwise again,
then into whatever size pieces you like (1⁄4–1⁄2″)
Transfer into a medium or large mixing bowl
Add 1 tsp salt, 1 tsp pepper, a shake of cayenne, and ~1⁄2 cup vinegar to finish the dressing (the amount of vinegar you add depends on how much bacon fat there is, it should balance)