Preheat oven to 350 F (180 C) for a convection oven. If you have a top and bottom heat oven, lower the temperature by 20 degrees. You can use 8 1 /2 x 4 1/2 inches loaf pan or 9 x 5 inches loaf pan. Oil the loaf pan and line with parchment paper for easier release
Please make sure the butter, eggs, banana puree, and carrots are at room temperature before you start working on the recipe. I usually take them out an hour before I plan to start. If it's warmer where you are, you may not even need that long
Combine all the dry ingredients in a bowl with a whisk
Use a hand mixer or a stand mixer to cream the butter and sugar until the mixture is pale, creamy, and fluffy. Then add egg, one at a time and continue to beat until it's creamy before adding another egg. Then add the banana puree and the grated carrot and mix until combined
Add the dry ingredients. Use the whisk to combine the mixture first so that the dry ingredients won't "fly" when you start the mixer. Start the mixer at the lowest speed just to combine. It won't be thoroughly combined, that's fine. We don't want to overmix. Use a rubber spatula to clear the side of the bowl and fold the dry ingredients until you don't see any more pockets of flour. This is a very thick batter
Scoop the batter into the prepared loaf pan and use flexible spatula to smooth the surface. Arrange about 10 large pieces of walnuts on top. Chopped walnuts are fine too
Baking:
Place the pan on the middle rack and bake for 45-50 minutes or until a cake tester inserted comes out clean. The time is just for reference, you will know your oven better. Start checking at around 45 minutes
Let the cake cool down in the pan for 10 minutes and then remove from the pan to a cooling rack and let it cool down completely
Serving:
I can tell you that the cake won't taste as good on the same day you make it. It won't be as moist because the cake hasn't had time to "mature". If you can wait for 24 hours before you slice the cake, you will be rewarded with a moist cake with a nice aroma of banana and butter (it's the hardest thing to do! I'm very impatient too LOL)
Storing:
Let the cake cool down completely and then store at room temperature in an air-tight container for about 4-5 days
For longer storage, wrap the cake in cling wrap tightly and then in a foil and it can be kept frozen for up to one month for the best result. Simply thaw at room temperature for 30 minutes or so before serving