This dip is reminiscent of the French onion dip in a plastic tub that we used to have at parties when I was growing up.
Technique tip: Make sure you gently cook the onions and add a bit of salt, which will help pull out the moisture in the onion and intensify its sweetness.
Cook the bacon in a large skillet over medium, stirring occasionally, until crisp, about 8 minutes. Transfer with a slotted spoon to a plate lined with paper towels. Reserve 3-4 tablespoons of drippings in the skillet.2.
Add the oil to the bacon drippings, and increase the heat to medium-high. Add the onions, and cook, stirring frequently, until softened, about 3 minutes. Reduce the heat to medium-low, and cook, stirring occasionally, until deeply browned and very soft, about 30 minutes. Spoon the onions into a large bowl. Stir in the vinegar. Let stand until cooled to room temperature, about 30 minutes.3.
Add the sour cream, salt, pepper, 1 cup of the bacon and 1/4 cup of the chives to the onions; stir until well combined. Top with the remaining bacon and chives. Serve chilled or at room temperature with the potato chips.