In a medium bowl, combine sour cream, mayonnaise, celery salt, Worcestershire, salt and pepper and chill.
Heat the butter in a skillet over medium heat. Add onions and sauté 35-40 minutes, stirring occasionally until golden brown and caramelized. Add shallots to the onion mixture and sauté for 10 minutes more until deeply golden brown and fragrant. Set aside to cool.
Transfer onions to a cutting board and chop coarsely into small pieces. Combine sour cream mixture with onions and transfer back to refrigerator for 30 minutes to 1 hour.
Serve with chips or veggies (or both). Enjoy!