Turn the IP to 'Saute' mode in the 'More' setting.
Add the butter, followed by the onions, garlic and sage (or assorted herbs). Sauté for a couple of minutes until the sage releases its aroma and the onions turn translucent.
Add the cubed butternut squash and stir to combine it with the rest of the ingredients.
Add the chicken (or vegetable) stock and mix.
Put on the lid of the Instant Pot and turn the vent to ‘Sealing’ position, and switch to 'Manual' mode (Pressure Cook mode), in 'High' Pressure setting. Set the cooking time for 4 minutes.
Once the IP beeps, do a quick release, i.e. turn the vent from sealing to venting position to release the steam quickly. Once all the steam has released, the pressure valve comes down and the IP lid is safe to open.
Open the lid and using a spatula, break down the cooked squash to a puree-like consistency.
Now add the penne. Ensure that the penne is submerged under the liquid in order to let the pasta cook evenly.
Put on the lid of the IP, and with the vent in 'sealing' position, in 'Manual' mode, in 'High' Pressure setting, set the time for 5 minutes. Let the IP release steam naturally (Natural Pressure Release). Once the valve comes down, the IP lid is safe to open.
Open the lid and add the white pepper powder, nutmeg and paprika powder, followed by the parmesan cheese.
Add the milk and give it a good stir.
Serve warm.