Place your pressure cooker over high heat.Add the butter, onion and celery and saute until the onion turns translucent.Add the chicken, salt, pepper and chicken stock and stir well.Place the lid on the cooker, pressurize and reduce the heat to low.
Cook for 1 hour.Turn off the heat and leave the pressure cooker to depressurize for 15 minutes before removing the lid.Use a metal spoon to press the chicken against the sides of the pot to shred the meat.Place the pot over low heat and add the cream.Sprinkle the xanthan gum over the simmering soup and whisk for 5 minutes to ensure there are no lumps.Remove from the heat and serve topped with the chives.