Place the sweet potatoes, onion, and stock in a large soup pot. Bring to a boil and simmer until the sweet potatoes are very tender. Add the curry powder and allspice and cook for 5 more minutes.
Remove from the heat and add the cream. Purée in batches in a blender or food processor until smooth. Add more stock if the soup seems too thick. Season with salt and pepper.
Pour into individual bowls and garnish with the raisins and toasted almonds.