Blanch the beans so that they're still bright green and a bit crunchy, and toss with the vinaigrette just before serving. The recipe is from Dana Ewart and Cameron Smith, chefs and caterers in Canada's Okanagan Valley, in British Columbia. They serve it as part of their open-air feasts at God's Mountain Estate, a vineyard and B&B near Penticton.
7 or 8 medium cipollini onions or 1/2 white onion, peeled and sliced into thin half-moons
1/4 cup cider vinegar
Salt and pepper
2 pounds haricots verts (thin French green beans) or regular green beans, trimmed
1 tablespoon whole-grain Dijon mustard
About 1/3 cup extra-virgin olive oil
1/2 cup skinned toasted hazelnuts, coarsely chopped
How to Make It
Bring a large pot of well-salted water to a boil. Mix onions and vinegar in a small bowl; sprinkle with a pinch of salt.
Boil beans 3 minutes for crunchy beans or 5 minutes if you want them more tender. Drain; plunge into a bowl of ice water.
Drain vinegar from onions into another small bowl and whisk in mustard, 1/3 cup oil, and salt and pepper to taste.
Toss beans with 2/3 of onions, 2/3 of hazelnuts, and vinaigrette to taste. Sprinkle with remaining hazelnuts and onions.