Preheat the oven to gas 4 / 180c. Line the 12 hole baking tin with paper cases.
For The Cupcake Bases
Cream the butter and sugar in a large mixing bowl until light and fluffy using an electric hand mixer. Beat in the two eggs and then the mashed banana.
Fold in the flour and cinnamon and then the broken walnuts and sultanas.
Divide the batter between the paper cases (two thirds full) and bake the cakes on the middle shelf for 15-20 minutes until golden and springy to touch. (18 minutes is what works in my oven).
Allow to cool completely on a wire rack.
For The Coconut Icing
In another large bowl, spoon the coconut milk over the icing sugar a little at a time, beating it into a smooth paste. It should be like thick PVA glue (I know that's not appealing exactly - but you get the picture).
Spoon the icing over the cooled cupcake bases and stud with a banana chip and walnut half before serving.