*Method 1:* In a large bowl, whisk together the oil, yogurt, Worcestershire, garlic, salt, and pepper. Stir in the blue cheese and chives. Add the buttermilk (or milk) to reach your preferred consistency, whisking well to fully incorporate the ingredients.
*Method 2:* Add the oil, yogurt, blue cheese, Worcestershire, garlic, salt, and pepper to a blender or food processor. Blend until the ingredients are thoroughly combined, scraping down the sides as necessary. You may blend until the dressing is smooth, or you may keep it a little chunky. Stir in the chives and milk to reach desired consistency.
Cover and refrigerate for one hour or until serving. Stored in the refrigerator, the dressing will keep for at least a week.