This may be prepared the night before and stored in the refrigerator.
Bring new potatoes, 1 tsp. salt, and water to cover to a boil in a Dutch oven; cook 18 to 20 minutes or until potatoes are tender. Drain and let cool.
Bring 2 qt. water and 2 Tbsp. salt to a boil in a Dutch oven; add beans. Cook 6 minutes or until crisp-tender; drain. Plunge beans into ice water to stop the cooking process; drain.
Combine green beans and potatoes in a large bowl. Pour Rosemary Vinaigrette over green bean mixture, tossing to coat. Cover and chill until ready to serve.