Place the potatoes in a large pot once sliced. Add enough water to the potatoes so that they are all covered.
Place pot onto the stove over medium high heat and cook until potatoes are fork tender.
Drain water from potatoes and set the potatoes aside to slowly cool.
Prepare the vinaigrette by combining the shallows, champagne vinegar and dijon mustard into a bowl. Slowly steam in the olive oil while whisking. Season with salt and pepper.
Transfer potatoes to a serving bowl and toss with the vinaigrette. Sprinkle with green onions and serve. (Can be served warm, at room temperature or chilled)