In the top of a double boiler, heat white chocolate over simmering water, stirring frequently, until melted and smooth. Remove from heat.

In the bowl of a stand mixer fitted with the paddle attachment, beat butter and salt at medium speed until smooth, 30 seconds to 1 minute. Beat in melted white chocolate, stopping to scrape sides of bowl. Reduce mixer speed to low; gradually add confectioners’ sugar, beating until combined. Add vanilla bean paste; increase mixer speed to medium, and beat until light and fluffy, about 2 minutes, stopping to scrape sides of bowl. Use immediately.