Chill the Coffee. Brew your coffee ahead of time and let it cool completely. Cold coffee gives the smoothie the best flavor and prevents it from becoming watered down by too much ice.
Add Ingredients to the Blender. Pour the chilled coffee into the blender, then add the banana, milk, Greek yogurt, peanut butter, cocoa powder, vanilla extract, honey or maple syrup, and ice if using.
Blend Until Smooth. Blend on high speed until the smoothie is thick, creamy, and completely smooth. Make sure there are no large ice chunks or banana pieces left.
Adjust the Texture. If the smoothie is too thick, add a splash more milk. If it is too thin, add a little more frozen banana or a few extra ice cubes and blend again.
Serve Immediately. Pour into a glass and enjoy right away while it is cold and creamy.