Beat the butter on high speed about two minutes until fluffy. Add in 1 cup of powdered sugar and beat on low just until mixed. Add the melted white chocolate and vanilla. Beat on low until combined. Add the remaining powdered sugar 1 cup at a time and mix on low speed until the mixture reaches your desired consistency.
Recipe by the modern barista at https://themodernbarista.com/index.php/2015/10/12/white-chocolate-mocha-via-latte-cupcakes/