Cut up your frozen bananas, so they'll blend more easily. Add them to your blender or food processor.
Add in cocoa powder to taste (start slow, you can always add more!).
Now, add in the smallest possible amount of your chosen milk. If you have a food processor (I use this one) or high speed blender. If you do add liquid, you want to add just enough liquid that you're able to blend the frozen bananas. Blend, and add more liquid as needed.
Serve up your smoothie bowl into chilled bowls and add your toppings