To a medium bowl add mayonnaise, sour cream, garlic powder, onion powder, dried parsley flakes, celery salt, white pepper [black if you prefer] and a few dashes worcestershire sauce.
Whisk together then fold in the blue cheese by hand. Reserve a few crumbles for garnishing.
Taste and adjust salt and pepper if needed.
Chill for at least 4 hours or overnight before serving.
Notes
To transform this dip into salad dressing, thin with buttermilk, milk or half and half until your desired consistency is reached.