Peel the potatoes and cut them into 1/2-inch cubes. Bring a large pot of salted water to a boil, then add the potato cubes and cook for 5-6 minutes until just tender but still holding their shape—they should be cooked through but not mushy. While the potatoes cook, mince the onion finely, dice the celery into 1/4-inch pieces, cook and crumble the bacon, hard-boil and chop the eggs if not already done, snip the fresh chives, and measure out all remaining ingredients. Drain the potatoes, reserving 1/3 cup of the cooking liquid (or use chicken stock if you prefer).

While the potatoes are still warm, combine the apple cider vinegar with the reserved 1/3 cup potato cooking liquid (or chicken stock), then pour this mixture over the drained potatoes. This is the key to Julia's technique—the warm potatoes will absorb the tangy liquid, developing flavor throughout. Let the potatoes sit undisturbed for 10 minutes to fully absorb the dressing. I like to do this step while the potatoes are still steaming because the warmth helps them soak up the flavors better than if they were cool.

After the 10-minute resting period, add the minced onion, diced celery, crumbled bacon, pickle relish, chopped hard-boiled eggs, and fresh chives to the potatoes. Gently fold everything together with a wooden spoon or spatula, being careful not to break up the potatoes. The goal is to evenly distribute all the ingredients while keeping the potato cubes intact.

In a small bowl, whisk together the mayonnaise, sour cream, and Dijon mustard until smooth and well combined. This creamy dressing base should be uniform with no streaks. Pour the dressing over the potato mixture and gently fold it in until all the potatoes are coated and the dressing is evenly distributed. Taste the salad and adjust the seasoning with salt and white pepper as needed—I find that starting with 1/2 teaspoon of each and tasting before adding more gives you better control over the final flavor.