1. Bring potatoes and salted water to cover to a boil in a large saucepan; reduce heat, and simmer 7 to 10 minutes or until tender. Drain. Place potatoes in a large bowl; sprinkle with vinegar and oil, and toss gently. Cool completely (about 1 hour).
2. Whisk together buttermilk and next 3 ingredients. Stir in carrots and next 6 ingredients; season with salt and pepper to taste. Spoon buttermilk mixture over potato mixture; toss gently to coat. Cover and chill 1 to 24 hours before serving.
Note: We tested with Kraft Reduced-Fat Mayonnaise with Olive Oil.