Preheat the oven to 180C / 160C fan and grease a loaf tin with the extra butter.
In a large mixing bowl cream the butter and sugar together until smooth and a little paler in colour. Add one egg at a time and beat well until fully incorporated.
Sift in the flour and spices and fold in with a wooden spoon then add the milk a bit at a time until smooth. Fold in the mashed banana, walnuts and chopped banana chips and mix well once more.
Spoon the mixture into the greased loaf tin level and place the remaining banana chips on top in a neat(ish) fashion.
Bake for about 1 hour. Check by placing a skewer into the center of the loaf and if it comes out clean it is ready. Some ovens vary and the loaf may take slightly longer and if you see the loaf browning too quickly cover loosely with foil.
Allow to cool in the tin for about 20 to 30 minutes before turning onto a plate.
Serve at room temperature or toasted with a good layer of butter and a cuppa.