Cut pumpkin into fourths; remove and discard seeds and strings. Place pumpkin pieces in a large, deep roasting pan. Add water to a depth of 2 inches.
Bake at 350° for 2 hours or until tender. Cool, peel, and cut into cubes.
Process pumpkin cubes, in batches, in a blender or food processor until mixture is smooth, stopping to scrape down sides. Divide puree into desired portions, and freeze up to 3 months.