Combine oil and butter in a large suacepan over medium heat. Add squash, onion and garlic. Cook for about 5 minutes, stirring occasionally, until crisp-tender. Add allspice; cook just a minute more. Add broth. Bring to a boil; cover. Reduce heat to low; simmer for 15 minutes or until squash is tender.
Process in a food processor until smooth. Return to saucepan; heat until hot. If a thinner soup is preferred, add a little more broth or water. Ladle soup into soup bowls. Garnish, if desired. Serve with crackers.