Make coffee ahead and let it cool completely. Store in the fridge.
Freeze a peeled banana for at least 2 hours.
Put frozen banana pieces in the blender.
Add cold coffee and milk.
Add peanut butter, cocoa powder, and honey.
Add ice cubes and protein powder if using.
Blend on high for 45 to 60 seconds until smooth.
Check thickness. Add more milk if too thick or more ice if too thin.
Pour into a glass and drink immediately.