Makes about 1/2 cup
In a small nonreactive bowl, whisk together vinegar, shallot, salt, pepper, and mustard. Allow to sit for 5 minutes to allow flavors to blend. While continually whisking, add oil in a thin, steady stream until completely incorporated and dressing is emulsified. Taste and adjust seasoning if necessary.
Cook's Note: Drizzle on a simple lettuce salad such as mixed spring greens.