Years ago I babysat for a family in the restaurant business. Everything they served was made fresh in-house. I loved their roquefort dressing. I believe they used similar ingredients. When I made it at home, I used blue cheese in place of roquefort.
Don't remember the proportions, but it was crumbled cheese (blue or roquefort), sour cream, mayonaise, milk, lemon juice, crushed fresh garlic and chives (or finely minced green onion). Best on the second day.