For salad: Preheat oven to 400 degrees. Wrap each beet in aluminum foil and roast for 60-75 minutes. The skin should rub right off leaving you a perfectly shaped baby beet. (I usually use a paper towel to avoid purple fingers!). Cut beets in half or quarters if larger. Arrange lettuce on plates and top with beets, walnuts and goat cheese. Drizzle with balsamic vinaigrette.
For vinaigrette: In a small bowl, whisk the mustard with the vinegar, shallot, if using, and salt and pepper to taste. Slowly pour in the olive oil while continuing to whisk until blended.