Preheat the oven to 180°C, fan 160°C, gas 4. Toast the walnuts on a baking tray for 8 minutes, then cool. Put the raisins in a small heatproof bowl, cover with boiling water and leave to soak and plump up while you prepare the cake mixture. Lightly grease and line a 900g loaf tin (with a base measurement of roughly 9cm x 20cm).
Mash the bananas in a large mixing bowl, then add the eggs, oil and sugar and beat with an electric mixer until pale and slightly thickened. Sift in the flour, bicarb, salt and spices. Fold in along with the flaxseed using a large metal spoon, but don’t overmix – a few lumps are fine. Drain the raisins and add to the batter with the carrot, milk and most of the pumpkin seeds and walnuts (reserve about 1 tablespoon of each for the top of the loaf).
Scrape the batter into the prepared loaf tin and level the surface. Combine the reserved pumpkin seeds and walnuts with the extra sugar, then scatter over the cake batter for a crunchy topping.
Bake for 1 hour to 1 hour 10 minutes, or until a skewer inserted into the loaf comes out cleanly with no sticky cake mix attached (a bit of moisture from the bananas, raisins or carrot is to be expected).
Cool in the tin for 10-15 minutes, then turn out onto a wire rack. Slice when completely cool.
