Using chopping/mixing blade with the food processor running, add red onion, mayonnaise, sour cream, dill, salt and black pepper through the food chute until onion is finely chopped and mixture is blended. Stop processor.
Add celery and pulse until coarsely chopped. Stopping processor and scraping bowl as needed, add shrimp through the food chute and pulse until chopped.
Cover and refrigerate for several hours to blend flavors.
Using chopping/mixing blade with the food processor running, add red onion, mayonnaise, sour cream, dill, salt and black pepper through the food chute until onion is finely chopped and mixture is blended. Stop processor.
Add celery and pulse until coarsely chopped. Stopping processor and scraping bowl as needed, add shrimp through the food chute and pulse until chopped.
Cover and refrigerate for several hours to blend flavors.