Preheat your oven to 400°F. Cover a half sheet pan with aluminum foil (optional) and spray a thin layer of non-stick cooking spray on to the foil (or pan) to prevent sticking. 

Remove the stem from the pumpkin and cut the pumpkin in half. 

Use a wide spoon to scrape out the seeds and fibers inside. Discard the seeds or clean them thoroughly for roasting later.

Lay the pumpkins onto the pan and roast for 45 min-1 hour. The pumpkin skin will take on a rust color when it's fully roasted and will feel soft to the touch.

Remove the pan from the oven and allow the pumpkin to cool for 10 minutes as they are. 

Peel off and discard the skin, then allow the pumpkin to cool completely. 

Puree the pumpkin in batches to achieve the smoothest puree possible.

Use your pureed pumpkin right away, or pack it into plastic freezer storage bags and freeze for later use.