Heat the butter in a large saucepan, add the onion and fry gently for 5 minutes until softened. Add the pumpkin, toss in the butter and fry for 5 minutes, stirring.
Mix in the orange rind and juice, the stock and star anise. Season with salt and pepper and bring to the boil. Cover and simmer for 30 minutes, stirring occasionally until the pumpkin is soft. Scoop out the star anise and reserve.
Allow the soup to cool slightly, then purée in batches in a blender or food processor until smooth. Pour back into the saucepan and reheat. Taste and adjust the seasoning if needed.
Ladle the soup into bowls and garnish each bowl with a whole star anise and a sprinkling of black pepper, or a slice of spiced orange and chilli butter. Serve with sesame bread rolls.