I made this roasted (and delicious!) pumpkin with a smaller sized one. It weighed roughly half of the size mentioned in the recipe but it still need a good 1 hr and 15 minutes to roast and even then the sides were cooked but the bottom not entirely.
Heat oven to 150C/130C fan/gas 2. Cut lid off pumpkin and scoop out seeds and strands. Put the pumpkin on a baking tray. Meanwhile, heat the cream, milk, garlic and most of the thyme, with plenty of seasoning. When hot, pour into the pumpkin and stir in 50g of the Parmesan. Put on the lid.
Bake for 1½ hrs, take from the oven, then turn up the heat to 200C/180C fan/ gas 6. Remove the lid, sprinkle with pepper and the rest of the cheese, then bake for 15 mins more until golden. Scatter over the remaining thyme leaves. Scoop the pumpkin flesh into bowls with the cheesy cream and serve with crusty bread as a starter.