Preheat your oven to 400°F (200°C). Wash your pumpkin, scoop out the seeds, and cut the pumpkin into wide wedges.
Put the pumpkin wedges skin-side down on a roasting pan. Brush the tops of the pumpkin wedges with olive oil. I used one tablespoon of olive oil per 2.5 lbs. (1.1 kg) of pumpkin (approximately)
Roast the wedges for 40 minutes until the pumpkin flesh is very soft.
After roasting the pumpkin, tent it in foil for 10-15 minutes to let it steam a bit. Now, scrape the pumpkin out of its skin into a food processor. I was able to peel the skin of the pumpkin off with my fingers. Very little was wasted.
Puree the roasted pumpkin until completely smooth. If you are using a large pumpkin, you will most likely need to do this in batches.
After pureeing, put the pumpkin in a dry cast iron skillet over medium heat. Let the water evaporate off of the puree, stirring frequently. The pumpkin will get thick like tomato paste. This will take approximately 10 minutes, depending on how watery the pumpkin you started with was.
Let your thickened pumpkin puree cool and then measure out ⅔ cup to make this pumpkin spice nice cream. You can freeze the rest of your pumpkin to use in other recipes.
Now, take your cooled pumpkin puree, and blend all of the nice cream ingredients together in a food processor until smooth. You may need to stop the processor and scrape down the sides with a spatula if ingredients are sticking.
Divide your ice cream into two bowls and enjoy as a soft serve. For a firmer nice cream freeze for one hour before scooping.