Serving poached vegetables in vinaigrette sauce is one of the French techniques that Julia Child popularized and America embraced. It has become less popular in our current era of grilled vegetables and high-protein salads. But sweet spring asparagus is particularly well suited to a nice soak in a shallot-scented dressing.
Note: Peeling the asparagus makes it more tender and refined, but it's not essential to the success of the dish.
Fill a 3- to 4-quart saucepan with about 1-½ inches of water and set a steamer basket in the bottom. Add asparagus, cover, and set over high heat. Steam until crisp-tender, 5 to 10 minutes depending on the thickness of the stalks. Immediately submerge the stalks in cold water. When cool, drain and transfer to absorbent paper. Pat the stalks dry and arrange them in a large serving dish. Sprinkle with salt and pepper.
In a small mixing bowl, whisk together the lemon juice and mustard until the mustard is dissolved. Whisk in the olive oil. Stir in the shallot and chervil. Pour the mixture over the asparagus and turn to coat the stalks. Cover the dish with plastic wrap.
Refrigerate until thoroughly chilled, about 45 minutes, turning the asparagus occasionally. To serve, arrange the asparagus spears on glass plates and spoon some of the dressing over the top.