Homemade pickle brine is whisked into a sensational vinaigrette for this light, tangy potato salad.
In a large pot, cover potatoes with 2 inches of cold water. Add 1 tablespoon salt. Bring to a boil, then reduce heat to a simmer and cook until potatoes are tender when pierced with the tip of a knife, 6 to 8 minutes. Drain; let cool 15 minutes.
While still warm, toss potatoes with pickled beets and onion, oil, celery seed, and 2 tablespoons brine. Season with salt and pepper. Let stand at room temperature at least 1 hour, or up to overnight in an airtight container in refrigerator. Just before serving, taste and adjust seasoning with salt, pepper, and brine. Serve, garnished with scallions, or refrigerate in an airtight container up to 2 days.