While beef broth might seem like an unexpected ingredient, it's a must for authentic German potato salad. Mixed with sauteed onions, it gives the vinegary slices of Yukon Golds an extra savory touch.
Peel potatoes, and place in a large pot with enough water to cover by several inches. Bring to a boil over high heat, add 1 tablespoon salt, and reduce to a gentle boil. Cook until potatoes are tender when pierced with a knife, about 10 minutes.
While the potatoes cook, combine the vinegar, sugar, and remaining 2 teaspoons salt in a small saucepan, and place over medium heat until the sugar is dissolved.
Drain potatoes into a colander. Using gloves or paper towels to protect your hands, slice the hot potatoes into 1/8-inch-thick rounds. Drizzle with hot vinegar mixture, gently stirring until all potatoes are coated. Set aside.
Saute bacon in a large skillet placed over medium-low heat, stirring frequently, until browned and crispy. Remove with a slotted spoon; transfer to a plate lined with paper towels. Drain excess fat from skillet, leaving a thin coating in bottom. Add onions; saute until translucent but not browned.
Add beef broth; bring to a boil over high heat. Reduce to a simmer, and cook until reduced by half, about 20 minutes. Pour over the reserved warm potato mixture, and sprinkle with the reserved bacon and chopped parsley. Gently stir to combine, and serve immediately.
You can substitute small regular Yukon gold potatoes for the baby ones; adjust the cooking time accordingly.