1. Cook beans in large pot of boiling salted water until crisp-tender, 4 to 5 minutes. Drain well; cool. Toss beans, radishes, and prosciutto in large bowl. Whisk Sherry, mustard, and chives in small bowl. Gradually whisk in oil. Season dressing to taste with salt and pepper. Toss salad with enough dressing to coat. Using vegetable peeler, shave ricotta salata in thin strips over salad.
2. * Available at some supermarkets and at specialty foods stores and Italian markets.