Sliced the ends off of the squash, cut it in half and scoop out the seeds.
Cut each half of the squash into 4 pieces.
Place the trivet inside your Instant Pot and add 2 cups of water.
Add in the butternut squash on the trivet and attach the lid and ensure the valve is in the "sealing" position.
Set the Instant Pot to "pressure cook - manual high" for 15 minutes.
Once the Instant Pot has finished cooking, release the pressure manually by switching the valve to the "venting" position - be careful it might splatter and hot steam will come out of the top!
Remove the squash from the IP and gently remove the flesh off the squash,
With a fork or a potato masher, mash the squash until the lumps are gone and you get the texture you would like. If you want it smoother you can also use an electric mixer.
Continue by placing the squash into a large bowl. Add in the butter, so it melts into the mixture.
Continue by adding the salt, pepper, sour cream, mix until combined and serve.
Optional: garnish with fresh rosemary, chives, or basil.