In a large saucepan, bring several quarts of water to a boil. While waiting for the water to heat, whisk the lemon juice, mustard and salt and pepper to in a small bowl. Whisk in the oil until the dressing is smooth.
Add asparagus and desired amount of salt to the boiling water. Cook until spears are tender but not limp, about 4 minutes.
Drain the asparagus in a single layer on a large platter. The asparagus can be covered with plastic wrap and refrigerated for several hours. When ready to serve, rewhisk the dressing and drizzle over asparagus. Serve immediately.