Place the potatoes in a saucepan and cover them with salted water; bring to a boil and cook until about half way done, 5 to 6 minutes. Drain and set aside to cool.
Meanwhile, make the vinaigrette: combine all the ingredients together in a glass measuring cup and whisk vigorously until well combined and slightly emulsified.
Combine the blanched potatoes and green beans in a bowl; add half the vinaigrette and toss to coat.