If you can't find haricots verts (small, thin French green beans), use regular beans. Make ahead: Blanch the beans up to three days before, wrap them in damp paper towels, and store in a zip-top plastic freezer bag. Compose and dress the salad just before the big feast.
Makes 6 servings
1. Prepare Pickled Onions: Toss together first 4 ingredients and 1/4 cup water in a bowl. Cover and chill 1 to 12 hours.
2. Prepare Vinaigrette: Whisk together cider vinegar and next 4 ingredients. Add oil in a slow steady stream, whisking constantly until smooth.
3. Prepare Salad: Cook beans in 6 qt. boiling salted water in a large Dutch oven over medium-high heat 3 minutes or until crisp-tender; drain. Plunge beans into ice water to stop the cooking process; drain and pat dry.
4. Cut hearts of palm into 1-inch-thick slices, and separate into rings. Toss haricots verts and hearts of palm with vinaigrette; add salt and pepper to taste. Arrange on a platter. Drain onions, and sprinkle over salad. Gently toss, if desired, and serve immediately.