1Preheat the oven to 170°C/Gas Mark 3. Cut the pumpkin in half horizontally and remove the seeds. Sprinkle salt and ground black pepper over it. Rub with the garlic halves and place the rosemary. Drizzle a bit of oil and put into the baking tray. Roast the pumpkin halves for about 1 hour until tender.
2Take out the rosemary and garlic; reserve the garlic. While still hot, scoop out the pumpkin flesh and purée in a blender or food processor.
3For the soup, heat the olive oil in a large saucepan, add the onion and cook for 5–6 minutes until soft and translucent and then put the mushrooms and cook for another 2 mins.
5Scoop out the flesh from 2 or 3 roasted garlic cloves and add to the pan with the nutmeg and a little seasoning. Sauté for a further 1–2 minutes.
6Stir in the pumpkin purée and Parmesan, then pour in the stock. Bring to the boil, lower the heat and simmer for 10–12 minutes.
7Stir in the cream and heat for a minute.
8In batches, ladle the soup into a blender and blend until smooth. Add the butter and blitz again to a velvety smooth texture.