Toss the trimmed asparagus with 2 tablespoons of olive oil, salt & pepper. Roast in a 400 degree oven for 12-15 minutes, until tender.
In a small bowl, whisk together 3 parts olive oil, one part balsamic vinegar, and one half part Dijon mustard. Sprinkle in salt & pepper to taste.
Allow the asparagus to cool to room temperature and drizzle with vinaigrette.