Mix 8 tablespoons milk with cocoa powder. Heat remaining milk in a pot with cardamom pods. Let steep about 10 minutes.
Remove cardamom. Stir in cocoa and milk mixture, sugar, espresso powder and salt and bring to a boil. Let cool.
Peel and chop bananas. In a blender, puree cocoa and bananas until smooth. Pour into glasses and serve garnished with banana slices and mint.