Warm Potato Salad with Arugula

2 lbs. Red Dog Farm Yukon Gold potatoes
1/4 cup extra-virgin olive oil
Salt and freshly ground pepper
1.5 tablespoons grainy mustard
1 tablespoons sherry vinegar
1 small Red Dog Farm sweet onion, thinly sliced (or substitute chives)
1/4 lb. Red Dog Farm baby arugula
Preheat the oven to 425°. Cut the potatoes into 1/2-inch wedges. Scatter the potato wedges on 2 large rimmed baking sheets, drizzle with 2 tablespoons of the olive oil and toss until coated. Season with salt and pepper and roast for about 25 minutes, until browned and crisp. In a small bowl, whisk the remaining olive oil with the mustard and vinegar and season with salt and pepper. In a large bowl, toss the potatoes with the onion and arugula. Top with the dressing, toss again and serve right away.