Preheat the oven to 300 degrees F (150 degrees C).

Cut pumpkin into small manageable pieces; cut off pith and seeds and discard.

Place cut pumpkin, skin-side up, in a large roasting pan. Add 1/4 inch of water.

Bake, uncovered, until tender, about 1 hour. Remove from oven and let cool for 10 to 20 minutes.

Cut skin away from cooled pumpkin pieces. Transfer pumpkin flesh to a food processor and puree until smooth, or mash pieces in a bowl with a potato masher.