I love cocoa, especially the good* stuff. This shake can also be used as starting point for lots of variations:
recipe for 1, can easily be adapted for more
1 ripe banana
handful of frozen blueberries
a few slices of frozen peach
small handful of raw cashews
1-2 T of good cocoa powder
1 cup milk (1% or higher, or milk alternative)
Start with just enough milk to cover fruit, adding more if desired; shake should be thick. Blend together, and enjoy in a tall glass with a straw.
*Callebaut has a really rich chocolate flavor and I can get it in bulk at Central Market for a great price. If you can't find it, I also like Hersey's special extra dark.