Notes: Up to 2 days ahead, make and chill maple-mustard sauce. One day ahead, cook beans; drain and immerse at once in ice water until cold. Drain again, wrap airtight, and chill. To reheat, immerse beans in boiling water to cover, remove from heat and let stand about 1 1/2 minutes, then drain. Or put beans in a microwave-safe bowl and reheat, uncovered, in a microwave oven at full power (100%) until steaming, 2 to 4 minutes.
2 pounds green beans, ends trimmed
2 tablespoons coarse-grain Dijon mustard
3 tablespoons balsamic vinegar
1 1/2 tablespoons maple syrup
2 teaspoons extra-virgin olive oil
2 tablespoons chopped green onion (including green top)
Salt and fresh-ground pepper
How to Make It
In a 4- to 5-quart pan, bring 2 quarts water to a boil over high heat. Add beans and cook, uncovered, until tender-crisp, 5 to 8 minutes; drain and pour into a bowl.
Meanwhile, mix mustard with vinegar, maple syrup, and oil. Pour over hot beans and mix to coat well; sprinkle with onion. Season to taste with salt and pepper.