2 tablespoons Sherry vinegar
1/4 cup extra-virgin olive oil
3/4 pound green beans, trimmed and cut into 1-inch pieces
1 shallot, thinly sliced
1 (19-ounce) can cannellini beans, drained and rinsed
Whisk together vinegar, oil, 1/4 teaspoon salt, and 1/8 teaspoon pepper in a large bowl.
Cook green beans in a 3- to 4-quart saucepan of boiling salted water 2 minutes, then add shallot and cook until beans are crisp-tender, about 2 minutes more. Drain in a colander and plunge into a large bowl of ice and cold water to stop cooking.
Drain well, then add to dressing in bowl along with cannellini beans and toss well.