Select a medium sized pumpkin that can fit into your pressure cooker. This is not the same as the pumpkin that you use for carving, as those are usually way too huge. You don't need to pierce your pumpkin before cooking or anything, and don't need to remove the stem either (but you could remove it if you prefer).
Place the steamer rack or basket at the bottom of your pressure cooker, then add 1 cup of water. Place your pumpkin on the rack/basket and cover with lid. Make sure that the lid is not touching the pumpkin.
Seal the pressure cooker, and cook on high pressure for 12 minutes.
When the cooking is done, let the steam release naturally. It will take around 10 minutes.
Open the lid, and let the pumpkin cool.
Lift the pumpkin out of the pot on a cutting board and cut in half. The flesh will be very soft and buttery.
Scoop out the seeds, and the skin will start peeling off very easily. Transfer pumpkin flesh to a food processor or blender and blitz until smooth. You could add a splash of water to make it easier to blend. I usually add around 1 tablespoon of water
Store in the refrigerator for up to 3 days, or divide in portions and freeze for up to 6 months.