Preheat oven to 400 degrees. Using a sharp paring knife, cut several slits in pumpkin, piercing skin all the way through (this will let steam escape). Place in a baking dish; pour about 1 inch water in bottom of dish. Bake until skin is easily pierced and inside is very soft, 1 1/4 to 1 1/2 hours.
Cut off top of pumpkin, and scoop out seeds; discard both. Peel, and discard skin. Place pumpkin in the bowl of a food processor; puree until smooth. Store in an airtight container in the refrigerator up to 2 days or in the freezer up to 1 month.
Store in the freezer up to 1 month.