Alternate layers of shrimp and onion in large bowl. Mix next 4 ingredients quickly with a handblender. Add celery seed, stir and pour over shrimp and onion. Cover and refrigerate for at least 24 hours. To serve, set out large bowl of shrimp and surround with small bowls/plates/cleaned clam shells and cocktail picks. Invite guests to scoop up a few shrimps and onions and eat out of bowls or shells. Great for patio parties. Recipe can be doubled.
Source: Eaton''s Great Canadian Recipe Challenge 1993