1 Peel the half banana, roughly chop and place in a high vessel. Add yogurt and milk and blend until frothy with an immersion blender.
2 Pour half the yogurt-milk mixture into a glass, add cocoa powder and grated chocolate and stir well.
3 Chop walnuts and stir into remaining yogurt-milk mixture. Pour mixture slowly over the back of a spoon into the glass. Serve with a thick smoothie straw.