Cook the barley in a large heavy-based saucepan of simmering water over medium heat for 35 minutes or until very soft; it should be overcooked so the grains are slightly overblown. Drain the barley and reserve 100 ml of the cooking water.
Blend the cooked barley, reserved water and butter in a blender (or Thermomix on speed 8) for 3 minutes or until smooth; the ba