Melt the dark chocolate in short bursts in the microwave or over a double boiler, then let it cool for a few minutes so it doesn't seize when it hits the cold ice cream.
Add the ice cream, milk, cocoa powder, melted chocolate, sugar, and salt to a blender.
Blend on high for 20–30 seconds until thick and smooth, stopping to scrape down the sides if needed.
Taste and adjust — add more milk for a thinner consistency or more chocolate for extra intensity.
Pour into a chilled glass, top with whipped cream and chocolate shavings, and serve right away.