Heat the white chocolate in 30 second increments in the microwave, stirring after each increment, and continue to heat 30 seconds at a time, until the chocolate is melted and smooth.
Set aside and allow to cool completely.
Using a mixer, cream the butter, salt and powdered sugar mixture together until light and fluffy.
Add the cream and vanilla to the butter/cream mixture using mixer at low speed until well incorporated.
Pour in the melted white chocolate until blended and then increase speed of mixer and continue beating on medium-high a few minutes.
Depending on consistency, add more cream or powdered sugar as needed for thinner or thicker frosting.
Makes about 3 & 1/2 to 4 cups of frosting.