Melt the white chocolate in a heatproof bowl set over a pot of simmering water. You need to make sure the bowl doesn't touch the water. You can also melt it in the microwave in 15-second bursts, stirring in between until smooth. Then let the chocolate cool to room temperature which should take about 15 minutes. You don't want the chocolate to melt the butter when mixed.

Check that the white chocolate is cool but still fluid. Slowly pour it into the butter mixture while continuing to beat on medium speed. Beat until the chocolate is fully incorporated (about 2 minutes). Your mixture should be smooth and creamy.

Add the heavy cream, vanilla extract, and a pinch of salt. Beat on medium speed for another minute. If the frosting is too thick, add more cream, 1 tablespoon at a time. If it's too sweet, a tiny bit more salt.

Your frosting is now ready to use! If not using immediately, store it in an airtight container in the refrigerator for up to 1 week or in the freezer for up to 3 months.