Preheat oven to 350°F (180°C)
Wash and scrub the pumpkin or squash, and put it on a baking sheet. You can line it with aluminum foil or parchment paper for easier cleaning afterward.
Baking it: it takes a while, at least an hour, sometimes half an hour more (it depends on the size and type of pumpkin) until it's fork-tender or can be very easily pierced with a knife. The inside should be very soft.
Remove from the oven and cut it in half.
Remove the pulp with a spoon and put it in the bowl of the food processor.
Processing: process until it's creamy. It will still be very wet, but that is fine.
Transfer to a colander set atop a bowl. You can add a cheesecloth before adding the pulp.
Draining: let the pumpkin pulp drain until the puree is thick. It will take a while.
Transfer the thick puree to a sealed container and keep refrigerated until ready to use. It keeps for several days.
Or keep it in the freezer for a month in an airtight container.