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 the oven to 180˚C (350˚F). Cut the lid of the pumpkin and scoop out any seeds and strands. Place the pumpkin on a baking tray and rub the insides with a little bit of oil, salt and pepper. Roast for about half an hour to get the proces started.
In the meantime, heat a small saucepan with a bit of olive oil and gently fry the garlic. Making sure not to brown the garlic. Add cream, milk and most of the thyme. Season generously. Turn the heat down in the oven after half an hour to 120˚C (300˚F) After half an hour add the hot cream into the pumpkin and stir in 50 gr of the grated parmesan. Put the lid on top of the pumpkin.
Roast for another hour or until you can easily insert a fork or knife on the inside of the pumpkin (don't poke a hole in the base however! You don't want any fluids leaking out) Turn the temperature up to 200˚C (400˚F). Remove the lid, sprinkle with pepper and the remaining parmesan.
Bake for another 15 minutes or until the top starts to brown slightly. Take out and sprinkle with the remaining cheese and black pepper. Scatter the thyme leaves over the top.
For serving you can serve in the pumpkin but easiest to scoop out the pumpkin flesh and serve it in separate bowls with the cream.