You can use freshly ground coffee as a garnish. For a stronger coffee note, increase the cold brew by 30 ml. Serve the dessert immediately after blending — longer processing will cause it to melt.
Frozen bananas combined with cold brew form a heavy, cold mass that overloads ordinary blenders or leaves unblended chunks. Thanks to variable speed control and the tamper, the Vitamix processes this consistency in under a minute into a uniformly creamy result. Start on the lowest speed and ramp quickly to maximum; use the tamper to push the frozen mass continuously toward the blades — the Ascent's Frozen Dessert program handles this ramp automatically.
Everything you need to know about technique and the right way to freeze bananas is covered in the guide How to Make Nice Cream.