Prepare the beets (if using fresh): If you have raw beets, cook them first. Trim and scrub whole beets, then boil in lightly salted water about 30–40 minutes (for medium beets) until easily pierced with a fork. Drain and let cool, then peel off the skins and cut the beets into small dice. (Note: You can also roast beets at 400°F until tender.) If using jarred pickled beets, simply drain and dice them.
Mix the base: In a large bowl, combine the diced beets with the chopped apple, diced onion, and chopped pickle (if using).
Whisk the dressing: In a separate small bowl, whisk together the mayonnaise and sour cream until smooth. Stir in 1 tablespoon of the reserved beet pickling liquid (or vinegar) and taste the mixture. The acid will help color the dressing pink. If desired, add up to 2 more tablespoons of brine/vinegar until the dressing is a bright rosy hue. (It’s better to add liquid slowly: too much can be balanced with a pinch of sugar.)
Toss the salad: Pour the dressing over the beet–apple mixture. Gently fold everything together so the vegetables are evenly coated. If needed, season with salt and plenty of pepper (the salad should be slightly salty-sweet).
Chill: Cover the bowl and refrigerate the salad for at least 1 hour before serving. Chilling allows the flavors to meld (and makes the color even brighter). The salad can be made a day ahead.
Serve: Give the salad a final stir. Garnish with chopped dill or parsley. Serve it cold as part of your Christmas spread. (See notes below for sandwich ideas or topping with sliced egg.)
