Preheat oven to 375 degrees F. Line a rimmed baking sheet with parchment paper.
Place the pumpkin halves on the baking sheet, cut side down. Roast until a skewer can easily pierce the flesh, 45 to 60 minutes. Turn the pumpkin halves over and roast for an additional 30 minutes.
Once cool enough to handle, scoop the flesh from the pumpkin skins and place in the bowl of a food processor. Puree until smooth, scraping down the sides of the bowl as needed, about 1 minute.
Place the pumpkin puree in a fine mesh sieve set over a medium bowl and allow to drain for at least 1 hour. To test the consistency, pack the puree into a small drinking glass and unmold it onto a plate. It should slump slightly but hold its shape. If it is too loose, return to the strainer and allow it to continue draining; if it is too firm, whisk in a little bit of the drained liquid.
Once the correct consistency has been achieved, you can store the pumpkin puree in an airtight container in the refrigerator for up to four days, or freeze (with parchment paper pressed against the surface of the puree) for up to two months. You can substitute this puree in equal amounts for any recipe calling for canned pumpkin.
Nutritional values are based on one ounce of puree