Combine the milk, vanilla bean and vanilla seeds in a saucepan and bring to a simmer. Remove the vanilla bean. Add the hot milk to the blender and carefully blend until frothy. Add the white chocolate to the blender and blend until the chocolate is melted. Divide between 2 mugs, top with a dollop of whipped cream and sprinkle with cocoa powder.
When blending hot liquid, first let it cool for five minutes or so, then transfer it to a blender, filling only halfway. Put the lid on, leaving one corner open. Cover the lid with a kitchen towel to catch splatters, and pulse until smooth.