Place whole mini potatoes in a large pot of cold, salted water. Bring to a boil over high heat and cook for 15-20 minutes, or until just tender. Drain and let stand 10 minutes or until cool enough to handle. Cut in half and place in a large bowl. Drizzle the vinegar over the potatoes and toss lightly. Sprinkle with a little salt.
Prepare the dressing by combining all the dressing ingredients in a medium bowl and stirring until smooth. Pour over potatoes and stir to combine. Season with additional salt and freshly ground pepper, to taste (be sure to salt generously to really bring out the flavours). Cover and refrigerate until well cooled, at least 2 hours. Garnish with additional green onion to serve.