Preheat oven to 180℃. Spray an 2-litre capacity (8 cup) baking dish with non-stick cooking spray.
Layer one third of the potatoes of the base of the prepared dish then layer over a half of the pumpkin. Sprinkle over half each of the chopped garlic, thyme leaves and chicken stock powder. Season well with salt and pepper.
Drizzle over ¼ cup of the thickened cream then repeat layering process finishing off with a potato layer. Pour remaining cream evenly over the top.
Take a sheet of foil that is larger than the dish your using. Spray with the middle section with non-stick cooking spray. Top with a smaller piece of baking paper that will just cover with top of the dish. Turn foil upside down so baking paper is facing the bench. Place over the top of the dish and seal, pushing the foil around the edges of your dish. Bake in the oven for 1 hour or until vegetables are tender (use a fork or tip of knife inserted in to check).
Remove from oven and discard foil and baking paper. Sprinkle the grated cheese evenly over the top. Return to the oven and bake, uncovered, for a further 20-25 minutes or until cheese is bubbling and golden brown. Remove and set aside to cool for 10 minutes before serving.