Cut the top off the pumpkin and discard the internal seeds and fibres.
Carefully hollow out the pumpkin flesh leaving a 2cm thick wall.
Roughly chop the removed pumpkin flesh.
Melt butter in a large pan and soften the onions for 15 minutes.
Add pumpkin, cinnamon, nutmeg, and seasoning, then cook covered for 45 minutes.
Add the stock, bring to a boil, then blend until smooth.
Simmer the blended soup in the pan for 30 minutes.
Preheat the oven to 170°C.
Pour the soup and sherry into the hollow pumpkin shell and stir.
Place the pumpkin lid on, set on a tray, and bake for 45 minutes.
Ladle the heated soup into bowls directly from the pumpkin shell.