Place water in the bottom of a steamer pot, and bring to a boil.
Set asparagus inside the steamer insert and cook, covered, for 4 to 6 minutes. Asparagus should be tender, but still maintaining its shape. Meanwhile, in a small bowl, whisk together mustard and vinegar.
Add the olive oil in a very thin stream, whisking constantly, until a thick emulsion forms. Place asparagus on a platter, drizzle with dressing, and top with shallots and pepper.