Add potatoes into a large stockpot and cover with cold water that extends at least 2 inches above the potatoes. Stir in a generous pinch of salt. Bring to a boil over medium-high heat. Reduce heat to medium, and continue cooking until potatoes are tender when pierced with a fork, about 15–20 minutes.

Meanwhile, cook bacon in a large saute pan over medium heat until crisp, stirring occasionally, about 10-12 minutes. Transfer bacon with a slotted spoon to a plate that has been covered with paper towels, and later break it into small pieces. Reserve 1 tablespoon of bacon grease in the pan, and discard the rest. Add onions to the saute pan and cook in the reserved bacon grease for 5 minutes, stirring occasionally, until cooked and translucent. Remove from heat and transfer onions to the plate with the bacon.

When the potatoes are cooked, drain them and cut into 1-inch cubes. Add potatoes to your serving bowl, and top with the cooked bacon, onions, vinegar, salt, and pepper. Toss to combine. Serve topped with fresh parsley.