Combine the squash, milk and chicken stock in a saucepan. Season with salt, pepper, curry powder, celery salt, cinnamon and nutmeg. Bring to the boil, then reduce heat to low and simmer for about 30 minutes, until squash is tender, stirring frequently to prevent the milk from scorching.
Add 1/2 the shrimp and 1/2 the pears to the soup and bring to the boil. Cook for 5 minutes or until prawns turn opaque. Transfer the soup to a liquidiser or food processor and blend until smooth. Return to the saucepan and bring to a simmer over medium-low heat.
Add the remaining prawns, remaining pears to the soup; simmer for another 5 minutes or until the prawns turn opaque. Stir in sherry and remove from heat. Ladle into bowls and garnish with a light sprinkle of cinnamon or nutmeg.