Place the vinegar and rosemary in a blender and blend until smooth. Slowly add the olive oil until emulsified and season with salt and pepper to taste. Strain into a bowl. Preheat grill. Toss potatoes in a large bowl with olive oil and season with salt and pepper to taste. Grill skin side down until golden, turn over and continue grilling until just cooked through. Place in a large bowl and immediately toss with 1/4 cup of the vinaigrette. Meanwhile, bring a large pot of salted water to a boil and add the haricots verts. Cook for 2 minutes, and immediately plunge into a bowl of ice water. Drain. Add the haricots verts and red onion to the potatoes and drizzle with the remaining vinaigrette. Season with salt and pepper to taste.
Recipe courtesy of Bobby Flay