French Potato Salad

1.Place small red potatoes and 1/2 tablespoon of salt in a large saucepan. Cover by 1 inch with cool water, then bring to a boil over high heat. Reduce the heat to medium and simmer until the potatoes are easily pierced with a knife, 15 to 20 minutes.
2.Place olive oil, red wine vinegar, Dijon mustard, whole-grain mustard, black pepper, and the remaining 1/2 teaspoon kosher salt in a large bowl. Whisk well to combine and emulsify.
3.Drain the cooked potatoes in a colander and rinse under cold water just until they are cool enough to handle but still warm. Halve the potatoes (or quarter if large) and transfer to the bowl of vinaigrette. Gently toss to coat the potatoes.
4.Add the parsley and green onions and toss lightly to combine. Set aside for 10 minutes to allow for the flavors to meld. Serve warm or at room temperature.