In a high-speed blender, combine coffee, milk, mint leaves, cocoa powder, cocoa nibs, vanilla, dates, and salt. Blend until smooth.
Add ice cubes and frozen banana pieces.
Pulse to crush the ice, then blend on high for 10 more seconds.
If needed, add more milk to reach your desired consistency.
Serve in tall glasses, topped with whipped cream and grated dark chocolate if desired.