Add 1 cup of water to the inner pot of your pressure cooker. Place a rack or trivet into the pot.
Cut the whole butternut squash into 3-4 pieces so that it fits on the rack. No need to peel the squash first.
Place the butternut squash pieces on the rack. Put the pressure lid on and turn the valve to seal. Pressure cook on high for 25 minutes. When the time is up, do an immediate release of the pressure.
Remove the squash pieces and place them on a cutting board or cooling rack. Peel away the skin, it will just fall off. Allow the butternut squash to cool slightly. Remove the seeds and strands from the bell part of the squash and discard or save to make roasted butternut squash seeds.
Using a blender, food processor, immersion blender, or a manual potato ricer, process chunks of the butternut squash until smooth. You should get about 1 cup of smooth puree per pound of butternut squash.
Use in your favorite recipes or freeze the puree for later use.