Spiced Butternut Squash Soup

1 medium butternut squash
2 T unsalted butter
1 medium onion, chopped
5 cups chicken broth
1/2 t ground nutmeg
1/4 t ground cloves
3/4 t salt
freshly ground black pepper

Melt butter in large pot. Add onion and sauté until translucent, about 10 minutes. Peel and seed squash; cut into 1-inch chunks. Add squash and broth. Do not add spices until later.  Adding them now will discolor the soup.  Bring to a a boil, reduce heat and simmer until squash is tender, about 15 to 20 minutes. Remove squash chunks with slotted spoon and puree in a blender. Return squash to pot and add remaining ingredients. Simmer several more minutes to blend flavors and serve.