Combine the butter, malted milk powder, salt, and 2 cups of the sugar in a large bowl and beat with an electric mixer on low speed until incorporated, about 1 minute.
Add the remaining sugar and beat on medium speed until the frosting is pale and no longer grainy, about 2 minutes. Add the vanilla and beat until the frosting is very light and fluffy, about 2 minutes.
Malted Vanilla Frosting will keep, in an airtight container in the refrigerator, for 1 week. Before using, bring it back to room temperature and stir it vigorously or beat it again for best results.