Heat the oven to 400 degrees F.
Slice a small piece of skin off the one side of the pumpkin so when laid on its side, the pumpkin will lay flat without rolling. Remove the stem and split the pumpkin in half from top to bottom, using a large cleaver and a mallet. Scoop out the seeds and fiber with a large metal spoon or ice cream scoop. Cut the fibers with kitchen shears if necessary. Reserve seeds for another use.
Sprinkle the flesh with kosher salt and lay the halves, flesh side down, on a parchment paper-lined half sheet pan. Roast until a paring knife can be easily inserted and removed from the pumpkin, 30 to 45 minutes. Test in several places to ensure doneness.
Remove the half sheet pan to a cooling rack and cool the pumpkin for 1 hour. Using a large spoon, remove the roasted flesh of the pumpkin from the skin to the bowl of a food processor. Process until the flesh is smooth, 3 to 4 minutes. Store in the fridge for up to 1 week or freeze for up to 3 months.
Recipe courtesy of Alton Brown, 2010