Preheat oven to 375°F. Wash and dry pumpkin. Remove the stem if desired or cut through it while cutting the pumpkin.
Using a sharp chef's knife (or other large kitchen knife), carefully cut the pumpkin in half vertically (from top to bottom or bottom to top). Scoop seeds out of each pumpkin half and save for roasting later.
Brush the cut side of each have with a little olive oil and place face down on a rimmed baking sheet. Roast at 375°F for about 60 minutes or until a paring knife easily pierces the shell of the pumpkin. The pumpkin shell should be darker and easily indented.
Remove from oven and let cool slightly. Turn the pumpkin halves over and scoop cooked pumpkin flesh out of the shell and into a food processor or blender with a spoon. Cover and process until smooth, scraping sides occasionally (about 2-3 minutes).
Use immediately in recipes, or refrigerate for up to a week in a clean, covered container. Puree may also be poured into clean freezer containers, covered, and frozen for later use.