Chop the onion into small pieces.

Combine all ingredients (chopped onion, vegetable oil, sugar, vinegar, ketchup, Worcestershire sauce, salt, prepared mustard, paprika, garlic powder, and celery seed) in a blender or food processor.

Process until the mixture is smooth and slightly thickened.

Transfer the dressing to a container with a lid.

Refrigerate for at least 1 hour to allow the flavors to meld.

Shake well before serving.