Heat the oven to 180C. Grease and line a 900g (2lb) loaf tin.
Peel the bananas and mash them in a large bowl. Dissolve the Chocolate Hazelnut spread in the hot milk, mixing until there are no lumps, then add the bicarbonate of soda. Pour/spoon this mixture into the bowl with the bananas, then add all the other ingredients except the nuts, and beat well with hand mixer.
Chop the nuts roughly leaving good sized chunks, then fold them into the mixture.
Fill the mixture into the loaf tin and bake for about an hour. It should be well risen and brown. Test with a skewer and if it comes out clean the cake is ready.
Turn it out and remove the lining paper. Leave to cool on a wire rack. Once the cake is cool make the icing/frosting.
For the Icing/Frosting
Melt the butter in a small pan add the cocoa and the chocolate hazelnut spread, stir to blend and cook gently for 1 minute. Stir in the milk and the icing sugar. Take off the heat and mix well, then leave to cool, stirring occasionally until the icing thickens.
Spread the icing over the top of the loaf cake with a wet spatula, don't worry if it looks a little bit oily, it will settle as it sets.
Chop the remaining cob nuts in half and place onto the icing to ensure an even coverage. Leave the cake for a couple of hours before cutting.
Notes
If you are not able to access Kentish Cobnuts then you can substitute hazelnuts or any other nuts.