For Dressing: Whisk first 5 ingredients in medium bowl. Gradually whisk in oil. Season to taste with salt and pepper. (Dressing can be made 1 day ahead. Cover and refrigerate. Bring to room temperature and rewhisk before using.)

For Salad: Steam potatoes until tender. Cool; cut into quarters. Cook green beans in large pot of boiling salted water until crisp-tender, about 5 minutes. Drain. Transfer beans to bowl of ice water and cool. Drain. Cut beans in half. Combine green beans, potatoes, onion and basil in large bowl. Add dressing; toss to coat. Season with salt and pepper. (Can be prepared 4 hours ahead; cover and let stand at room temperature.)

** When I can't find fresh beans, I use a package of frozen french style green beans and thaw in a colander (to allow draining of any excess liquid).