Instead of roasting just one pumpkin, try doing two at one time so you can have pumpkin puree even in May.
Preheat oven to 400 degrees. Snap off the pumpkin's stem and halve the gourd lengthwise. With a spoon or melon baller, remove seeds and rinse for roasting or discard.
Place pumpkin halves cut-side down on a large rimmed baking sheet. Roast until tender, about 1 hour.
When cool enough to handle, scoop out cooked pumpkin flesh; discard skin. Transfer pumpkin flesh to a food processor; process until smooth.
Set a colander in a large bowl and line with a double-layer of cheesecloth. Place pumpkin puree in cheesecloth. Cover with plastic wrap and place in refrigerator to drain, at least 4 hours, and up to 3 days.
Kept in the freezer, the puree will last for up to 6 months.