1In a large bowl, Whip the butter on high speed, occasionally scraping down the sides of the bowl. Whip until double in volume. This takes a very long time, approximately 10 minutes.
2While still whipping, drizzle in the heavy cream. Continue whipping until the mixture is stiff, approximately 2 to 4 minutes.
3Add 1/2 of the confectioners sugar and whip until smooth. At this point, you can taste the frosting and determine if you would like to add more sugar to sweeten to taste.
4Thickly frosts top and sides of two 9 inch cakes.