Potatoes make satisfying side dishes in all seasons, summer included. What would a picnic be without potato salad? Opinions on which ingredients are essential to potato salad can vary (maybe your must-include is hard-cooked egg, or diced onion, or sweet pickle relish). Regardless, the starting point must be a basic recipe that promises a good outcome every time. My stripped-down method does just that -- all the salad needs are creative additions to make it your own.
Set a steamer basket in a Dutch oven (or large pot with a lid), and add enough salted water to come just below basket; bring to a boil.
Place potatoes in basket, cover pot, and reduce heat to a gentle simmer. Steam potatoes, gently tossing occasionally, until tender, 15 to 25 minutes.
Meanwhile, in a large bowl, combine vinegar, scallion whites, 1 teaspoon coarse salt, and teaspoon pepper.
Add hot potatoes to vinegar mixture; toss to combine. Cool to room temperature, tossing occasionally, about 1 hour.
Add mayonnaise and scallion greens to cooled potatoes; mix gently to combine. Serve, or cover and refrigerate up to 2 days.