Heat oven to 400ºF. Line a half-sheet pan with parchment paper.
Slice a small piece of skin off one side of the pumpkin so when laid on its side, the pumpkin will lay flat without rolling. Using a large cleaver and a mallet, remove the stem and split the pumpkin in half from top to bottom. Scoop out the seeds and fiber with a large metal spoon or ice cream scoop, rinsing and reserving the seeds for another use. Cut the fibers with kitchen shears, if necessary.
Sprinkle the flesh with kosher salt and lay the halves, flesh-side down, on the prepared 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 wire 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.