Heat the butter in saucepan, add the onion and fry until softened. Add the pumpkin toss in the butter and fry about 5 minutes.
Mix in orange juice and rind, the stock and star anise. Season with salt and pepper and bring to boil. Cover and simmer for 20 minutes, stirring occasionally until the pumpkin is soft. Scoop out the star anise.
Allow the soup to cool slightly, then puree in a blender until smooth. Pour back into saucepan and reheat. Taste and adjust the seasoning if needed.