Put the coffee in a saucepan and bring to a simmer. Add the sugar and cocoa powder and whisk well until dissolved. Add the fluff and continue whisking until completely dissolved. Remove from the heat and cool to room temperature.
To make the shakes, put the ice cream into a large blender and pour the coffee syrup over it. Add 1 cup of ice and blend until smooth (Divide the ingredients in half and make in separate batches if necessary). If you like your shakes a little thicker, add more ice and blend until you reach the desired consistency. Pour into glasses, top with shaved chocolate and serve immediately.