Transfer mixture to bowl of stand mixer fitted with paddle attachment. (iwasborntocook.com)
In bowl of stand mixer fitted with paddle attachment, beat butter and both sugars on medium speed until light and fluffy, around 3 minutes. (iwasborntocook.com)
Combine butter and icing sugar in standing mixer fitted with paddle attachment, on low until blended (about 1 minute). (thefoodiechef.com)