Makes about 1 cup
In a nonreactive mixing bowl, whisk together vinegar, mustard, sugar, salt, pepper, and garlic. While whisking, add oils in a thin, steady stream until completely incorporated and dressing is emulsified. Use immediately, or refrigerate in a covered nonreactive container, up to 1 week.
Cook's Note: This vinaigrette is best if allowed to sit for at least 10 minutes to allow the garlic to infuse. (Discard the garlic before serving.)