Preheat the oven to 400°F.
Line a rimmed baking sheet with parchment paper.
Wash and dry the outside of the pumpkin.
Carefully cut the pumpkin in half from top to bottom.
Use a large spoon to scoop out the seeds and stringy pulp.
Set the seeds aside if you want to roast them.
Place the pumpkin halves cut side down on the prepared baking sheet.
Roast for 45 to 60 minutes, or until the skin looks wrinkled and a fork slides easily into the flesh.
Remove the pumpkin from the oven and let it cool for 15 to 20 minutes.
Scoop the soft pumpkin flesh away from the skin.
Add the pumpkin flesh to a food processor or blender.
Blend until smooth.
If the purée is watery, drain it in a fine mesh strainer or cheesecloth for 10 to 15 minutes.
Use right away, refrigerate for up to 1 week, or freeze for up to 6 months.