Place the milk in your blender first, followed by the dates and cocoa powder. Blend until completely smooth. Add the frozen banana slices, and blend again until smooth.
Serve immediately.
Store any leftover smoothies covered in the refrigerator. It may thin a bit as it sits, since the bananas will defrost, but should stay relatively thick.
Video
Notes
Nutrition information.Nutrition information is per serving, assuming you are using almond milk, and is approximate and should not be relied upon.