Preheat the oven to 180°C (160° fan) | 350F | gas 4. Grease and line the base and sides of a 900 g | 2 lb loaf tin with greaseproof paper.
Combine the flours, baking powder, bicarbonate of soda, and salt in a large mixing bowl, stirring well.
Beat together the butter and honey in a separate mixing bowl until pale and creamy, 2-3 minutes.
Beat in the eggs, one by one, until incorporated and then stir in the milk, vanilla extract, and mashed bananas.
Spoon the batter into the prepared loaf tin and rap on a work surface to help settle it.
Bake for about 1 hour until golden and risen on top; cover the top with aluminium foil if it starts to brown too quickly.
When ready, a cake tester should come out clean from the centre. Remove from the oven and leave to cool on a wire rack in its tin.
Melt the chocolate in a heatproof bowl set over a half-filled saucepan of simmering water, stirring form time to time.
Turn out the loaf from the tin and top with the nuts. Drizzle with the melted chocolate, letting it set before slicing and serving with peanut butter and sliced banana.
If possible, make sure that the four bananas that are mashed are very ripe; the fifth banana should be not be overripe as it will be sliced and served as a garnish.