Preheat oven to 350F and spray or grease and lightly flour a 9"x5"x3" loaf pan
Sift flour, baking powder and soda into a large mixing bowl, add salt and whisk. Set aside
In a medium bowl, mash the ackee (a whisk or a rubber spatula does this well, alternately, you could pass the ackee through a sieve or blend it). Add the brown sugar then the eggs followed by the brown butter mixing till well combined.
Make a well in the centre of the flour mixture and pour in the ackee mix along with the walnuts.
Gently mix till well combined. Pour into prepared loaf pan and smooth top with a spatula.
Bake for 30 minutes then reduce temperature to 325F and bake another 10 to 15 minutes till done - a skewer inserted in the loaf will come out clean and/or it will spring back when lightly touched.
Remove from oven and allow to cool in the pan for 15 minutes. Turn out of pan and let cool completely on a wire rack.
Slice and enjoy!