Combine cornstarch, salt, and ground black pepper in a shallow bowl. Dredge both sides of each pork steak in the cornstarch mixture.
Heat olive oil in a pressure cooker over medium heat. Cook pork steaks in hot oil until browned, 2 to 3 minutes per side. Add wine, carrots, celery root, parsley root, and prunes to the pressure cooker. Cover and cook at high pressure according to manufacturer's instructions, about 8 minutes. Remove from heat and release pressure through natural release method.
Open the pressure cooker carefully. Transfer carrots, celery root, parsley root, prunes, and cooking liquid to a blender. Cover and hold lid down; blend to the consistency of a thick gravy, 1 to 2 minutes. Pour over pork steaks.