Season the beef roast with salt and pepper, then add the olive oil to the pressure cooker to cook over medium heat (with Instant Pot, press the 'Saute' button to begin cooking at medium saute heat). When the oil is hot, place the meat into the cooker and brown well on the top and bottom surface (about 4-5 minutes on each side).
After both sides are browned, pour in the coffee and add the thyme and bay leaf. Arrange the potatoes and onion wedges around the meat, then place the halved butternut squash on top, cut sides up. Take care not to obstruct the pressure valve area.
Cover the pressure cooker with the lid, ensuring that the valve is in sealing position. Cook under high pressure for 45 minutes (with Instant Pot, press ‘Cancel’ to stop saute mode before closing the lid, then press ‘Manual’ and "+" to select 45 minutes).
When the cooking time is up, allow at least 10 minutes for the pressure to release naturally. Open the lid and carefully set aside both the butternut squash and the beef roast.
Turn the pressure cooker back on to saute on medium heat (with Instant Pot, press 'Cancel' to deactivate the keep-warm mode, then 'Saute' button to begin cooking at medium saute heat). In a small bowl, mix together a slurry of the cornstarch and water, and mix it into the cooking liquid. Allow the sauce to reduce, stirring frequently; when it reaches a pleasantly thickened gravy consistency, turn off the cooker and return the beef roast to the sauce.
Meanwhile, scoop the cooked flesh of the butternut squash into a medium bowl. Add butter and salt, mixing to combine.
To serve, use shallow bowls so the coffee gravy can be ladled over slices of pot roast and potatoes with the butternut mash. Garnish with chopped fresh parsley.