In a microwave safe bowl, melt the white chocolate in 30 second intervals, stirring well between each one (it took me three 30 second intervals). Set aside to cool.

In a medium bowl beat the butter on medium speed for 1 minute (use an electric hand beater or stand mixer fitted with the paddle attachment). With the mixer on low speed, slowly add the icing sugar (you made need to cover the bowl with a t-towel to avoid a cloud of icing sugar). Once the white chocolate is cool, give it a stir so that it is smooth and add to the butter/sugar mixture.

Beat for 2 minutes at medium speed until is is creamy and well combined.

Add the cream (or sour cream if using), vanilla extract, and salt. Beat until combined. Give it a taste and add more icing sugar or salt if needed.