Bring a large pot of heavily salted water to a boil over high heat. In the meantime, snap the stem ends off the beans and rinse them under cold water. Fill a bowl with ice water and set it near the sink.
When the water is boiling rapidly, add the beans to the pot. Cook them for a couple minutes, until bright green and just tender. Drain them and quickly transfer them to the bowl of ice water. Stir the beans around a little, and once they're cool, drain them again. Lay the beans out on a kitchen towel to dry completely. Cut the beans in half, or leave them whole if you prefer.
To make the vinaigrette, combine both the vinegars with the mustard, honey and a few generous pinches of salt in a small bowl. Whisk until smooth. Slowly drizzle in the olive oil, whisking continuously, until the dressing is emulsified. Taste and add more salt or honey if you like. You can also put all of the vinaigrette ingredients in a jar, seal it tightly and shake vigorously to combine -- which is what I usually do.
Put the beans in a bowl, add a few tablespoons of the vinaigrette and toss well. Taste and add more dressing if you like before serving. You can store the rest of the vinaigrette in the refrigerator for up to 2 weeks. Any leftover dressed beans will keep in the refrigerator for a few days -- as time passes, they absorb more of the vinaigrette and start to sort of half-pickle, which I actually kind of like.