How to Make It
In a blender, combine the cider vinegar with the shallot, mustard and salt and puree. With the machine on, gradually add the olive oil until blended, then mix in the boiling water.
In a large saucepan of boiling, salted water, cook the green beans until barely tender, about 4 minutes. Drain the beans and spread them out on a paper towel-lined baking sheet; let cool.
In a large bowl, toss the green beans with the tomatoes, apple, onion, parsley and chives. Add the dressing, toss well and serve.