In a blender mix together all ingredients, except the butter, for 5
seconds at high speed.
Reduce the speed to low and pour the butter
in a thin stream. It should take about 10 seconds.
If needed, whip
again at high speed for 5 more seconds.
Keep in warm water until
ready to serve, or reheat in a microwave oven at level 3 (defrost) for 3
minutes.