Place the potatoes in a large pot and cover with cold water by at least a couple inches. Salt the water generously, bring to a boil and cook until the potatoes are fork tender, about 20 minutes. Drain and rinse under cold water.
Bring another pot of salted water to a boil and throw the beans in just for a minute or two until they turn bright green. Strain them and run them under cold water to stop the beans from cooking.
In a mixing bowl combine the remaining ingredients and whisk until smooth.
Cut the potatoes in half lengthwise and then into roughly 1 inch chunks. Cut beans in half. Toss the potato chunks in the dressing and then toss in the green beans and the parsley.