Add all of the ingredients to a small food processor/food chopper. Pulse well, until the dressing is smooth and all ingredients are well combined.
1 cup mayonnaise, ½ cup sour cream, ½ tsp garlic powder, ¼ tsp salt, ⅛ tsp finely ground black pepper, 2-3 tsp anchovy paste, 2 tsp grey poupon dijon mustard, 2-3 tbsp lemon juice, ¼-½ cup Parmesan cheese, 2 green onions, 1 tbsp rice wine vinegar, 2 tsp white wine vinegar, 1 tsp white granulated sugar