Combine blue cheese, sour cream, buttermilk, mayonnaise, vinegar, olive oil, and sugar in a bowl; blend using a hand mixer. Taste, and add salt and pepper as needed. Chill until ready to serve.
Build the salad by placing 1 lettuce wedge on each of 8 plates. Drizzle equal amounts of dressing over each wedge of lettuce. Scatter tomatoes, bacon, and blue cheese over each salad, and garnish with fresh parsley.
(Nutrition information provided is an estimate and will vary based on cooking methods and brands of ingredients used.)