1 tablespoon white-wine vinegar
1 tablespoon Dijon mustard
Coarse salt and ground pepper
2 bunches watercress trimmed
1 cucumber, halved lengthwise and thinly sliced
In a large bowl, whisk together oil, vinegar, and mustard; season with salt and pepper. Add watercress and cucumber; toss to combine. Serve immediately.
Although watercress stems are edible, the bottom two inches are usually too tough for salad. Trim them off with a sharp knife