Put the pumpkin in a large roasting tin with the garlic cloves and toss with 2 tablespoons of the oil. Roast in a preheated oven, 200°C (400°F), Gas Mark 6, for about 30 minutes until the pumpkin is very tender and beginning to brown.
Meanwhile, heat the remaining oil in a large saucepan over a low heat. Add the onions and celery and cook for 10 minutes until just beginning to brown. Stir in the rice and stock. Bring to the boil, then reduce the heat, cover and simmer for 15–20 minutes until the rice is tender.
Leave the pumpkin and garlic to cool slightly, then pop the garlic cloves out of their skins and mash them with a fork. Add to the saucepan with the pumpkin and bring to the boil, then simmer for 10 minutes.
Roughly blend the soup in a food processor or blender and return to the pan. Season with salt and pepper. Add extra stock if too thick. Reheat and stir in the parsley. Serve with Parmesan Crisps (see below), if liked.