Put the cocoa, Equal, malted milk powder, banana and milk into a blender and puree until smooth. You may have to do this in two batches depending on the size of your blender.
Transfer the mixture to a pan and cook over a medium heat until hot, take care not to let it boil and spill over the pan. Divide the banana chocolate drink between four large mugs and top with marshmallows.
This drink is delicious hot or cold. It will separate on standing so stir well before serving. It can be kept in an airtight container and heated when required. Soy milk can be substituted for low fat milk.