I think the mixture needs to refrigerated during the 20 minute standing period. Usually it needs to be chilled to a spreadable consistency and then whipped until fluffy.
I hope this helps.:-)
I have tried this recipe twice now and both times it has never become fluffy (soft peaks). It was heavy and very loose today. It appeared to have too much butter in the recipe but I used exactly what the recipe called for, 3 Tablesppons. Can anyone provide any tips or advise? My husband loves the taste but it has yet to look like true frosting. Third time a charm???