I agree with gloria. Mix the icing and then place it in the
refrigerator to harden the butter. When it is stiff, place it back in
the mixer and wipe with the whisk attachment for a few seconds until
it is the consistency that you would like. If it is too hard, place
the bowl on top of a pan of boiling water for only a few seconds and
then whip...becareful...the boiling water will melt the butter really,
really quickly...