Methods/steps

1. Steam asparagus on steamer rack set over boiling water, covered, until just tender, 3-5 minutes (depending on thickness), then transfer to bowl of ice water to stop the cooking. 
2. Drain well and pat dry with paper towels. 
3. Whisk together vinegar, shallot, mustard, salt, and pepper in a small bowl and add oil in slow stream, whisking until emulsified. 
4. Whisk in tarragon. 
5. Halve egg and force each half through coarse sieve (or finely chop). 
6. Toss asparagus with 1 Tbs vinaigrette, and divide among 4 plates. 
7. Spoon remaining dressing over asparagus and top with egg.