Green Beans with Red Onion and Mustard Seed Vinaigrette

Ingredients

• 1.5 lb green beans trimmed
• 2 tablespoons mustard seeds 
• 3 tablespoons olive oil 
• 1 medium onion red thinly sliced
• 0.3 cup red-wine vinegar 
• 1 tablespoon sugar 

Equipment

• bowl
• frying pan
• sauce pan
• pot
• colander

Directions

1. Heat 1 tablespoon oil in a heavy skillet over moderate heat until hot but not smoking, then cook mustard seeds, stirring, until they pop and are 1 shade darker, about 2 minutes.
2. Transfer oil with seeds to a large bowl.
3. Simmer vinegar and sugar in a small saucepan, stirring, until sugar is dissolved, then cool 5 minutes.
4. Heat remaining 2 tablespoons oil in cleaned skillet over moderately high heat until hot but not smoking, then cook onion, stirring, until golden brown, 8 to 10 minutes.
5. Remove from heat and stir in vinegar, then add to mustard oil in large bowl.
6. Have ready a large bowl of ice and cold water.
7. Cook beans in a pot of boiling salted water until crisp-tender, about 5 minutes.
8. Drain in a colander and plunge into ice water to stop cooking, then drain well.
9. Toss beans with vinaigrette and salt and pepper to taste.
10. Serve at room temperature or chilled.