Preheat the oven to 400°F. Line a baking sheet with parchment paper.
Cut the pumpkin in half through the stem and scoop out all the seeds and membranes with a large spoon. Set those aside for roasting as a snack later.
Salt the flesh and place the pumpkin cut side down on the parchment paper. Roast for 35 - 45 minutes, or until the pumpkin is cooked through and can be easily pierced with a paring knife. Let cool for at least one hour.
Peel the skin off of the pumpkin flesh. Pour the water into the bottom of the blender or food processor and puree until smooth. Add more water if needed.
OPTIONAL: Transfer the pumpkin puree to a pot and cook out any excess moisture over low heat. Stir it regularly to make sure it doesn’t stick to the bottom or burn.
Transfer to an airtight container and refrigerate up to five days.
The optional step is for if you decide to use homemade pumpkin puree in place of canned. This helps get a consistency closer to what you would get store bought. The water is added to help move the blade through the purée, but it can make the final product excessively wet for baking.