1. Snap off and discard woody bases from asparagus. If desired, scrape off scales. In a covered medium saucepan cook asparagus in a small amount of boiling water for 2 to 4 minutes or until crisp-tender. Transfer asparagus spears to a bowl filled with ice water; set aside.
2. For dressing, in a food processor bowl or blender container combine rice vinegar, dry sherry, sugar, tarragon, mustard, salt, and pepper. With processor or blender running, slowly add oil in a thin, steady stream. (This should take about 1 minute.) Continue processing or blending until well mixed.
3. To serve, drizzle about half of the dressing over the greens; toss to coat. Divide greens among 4 salad plates. Pat asparagus dry with paper towels; arrange on top of greens. Drizzle asparagus with remaining dressing. Sprinkle with sesame seeds.