Butternut Squash Soup

1 medium butternut squash
1 medium onion, chopped
2 cloves garlic
6 cups chicken stock (or reduced-sodium broth)
2 tablespoons dry sherry
1/2 teaspoon ground ginger
1/2 teaspoon ground cumin
1/2 teaspoon ground cinnamon
1/4 teaspoon ground cloves
Salt and pepper to taste
Plain yogurt and chopped parsley, for garnish

To prepare the squash: Peel the squash with a vegetable peeler and trim each end. Cut the squash in half lengthwise and scoop out the seeds. Place squash flat side down on cutting board and cut each half lengthwise. Cut the quarters crosswise to make 2-inch cubes.
Put the squash and the remaining ingredients (except garnishes) in a large pot and bring to a boil over high heat. Stir briefly, reduce heat to medium low and simmer for 18 minutes, until the squash is just cooked through.
Puree the soup using a blender or food processor in four batches, using equal parts solids and liquid to help make a smooth puree. (Caution! Hot liquids create steam which will blow the top off the blender! Be sure to securely hold blender lid down!) Pour each batch of pureed soup into a large serving bowl or medium saucepan if not serving right away. Adjust seasonings.
To serve ladle soup into bowls and garnish each bowl with a dollop of yogurt and a sprinkling of parsley.
Serves 4.