In a heavy pot, cover the potatoes with water. Bring to a boil and cook until the potatoes are tender, about 40 minutes. Drain the potatoes. When cool enough to handle, peel and cut into ½-inch cubes. Return the potatoes to the pot.

Fry the bacon until crisp. Remove from the pan, reserving the bacon grease. Drain the bacon, then crumble. To the bacon grease in the pan, add the vinegar, salt, and pepper. Heat over medium heat until bubbling. Remove from the heat.

Pour the dressing over the potatoes. Reserve some scallions and bacon for a garnish and add the remainder to the potatoes. Toss lightly to mix. Cover and let stand for 45 minutes to absorb the seasoning.

Just before serving, set the pot over moderate heat and heat for about 10 minutes. Turn out into a serving bowl. Top with the reserved bacon and scallions and serve.