Black and green bean barley salad

Directions

1. In a large saucepan combine the barley with 4 cups boiling salted water and simmer, covered, for 45 minutes, or until it is cooked but still al dente. Drain the barley in a colander, rinse, and drain well.
2. In a small bowl whisk together the lemon juice, mustard, salt and pepper to taste, add the oil in a stream and whisk the dressing until it is emulsified.
3. In a large bowl combine the black beans, the barley, green beans and the onion, add the dressing, and toss the salad until it is well combined.
4. The salad may be prepared up to this point 1 day in advance and kept covered and chilled. Serve the salad chilled or at room temperature.