Put the sugar and butter in a large bowl (which should be left out of the fridge at least half an hour before so that it is soft and manageable). Beat well with a hand or electric stirrer until the mixture turns creamy.
Peel the bananas and mash them with a fork until the cream is as homogeneous as possible, although lumpy.
Preheat the oven to 180ºC for about 10 minutes while you finish the mixture.
Add the bananas and the eggs to the bowl and beat everything well so that the ingredients are integrated.
Chop the walnuts into small pieces, and if you have chosen to use chocolate for desserts, chop that as well. If, on the other hand, you are going to use chips or chocolate chips, you will not have to do anything to them.
Add the sifted flour , that is, passing it through a sieve so that it does not fall with lumps or cakes. Do the same with the cinnamon , baking powder and bicarbonate and also add the pinch of salt . Mix everything well again until the ingredients are mixed. You should know that between adding the baking soda and putting the cake in the oven, the shortest time possible should pass so that its bubbling effect is noticeable in the cake, airing it.
Finish by adding the chocolate chips and the slightly chopped nuts , and mix well.
Paint your mold with a little butter using a kitchen brush, or if you prefer, line it with greaseproof paper.
Pour the cake mixture with it and decorate it. Peel the remaining banana and cut it into slices. I like to cut them diagonally to make them bigger but you can also cut them round, and put them on the cake.
Sprinkle some flake salt , some chopped walnuts and some chocolate chips on top .
Place the mold in the oven at medium height, with heat up and down and a fan. Bake for 50-60 minutes or until done. You can tell if, from minute 45, you do the toothpick test : click the cake with a toothpick, and if it comes out with few remains stuck, it is ready. Be careful, I say "few leftovers" because it is a cake that you do not have to cook 100% or until it dries completely because there are always leftovers that are usually pieces of banana. If it is excessively soft to the touch and does not yet have a certain structure, leave it for a few more minutes.
Also keep an eye on it from minute 40 onwards because if it is browning too much on the top you should cover it with aluminum foil and continue baking it.
Turn off the oven, remove the cake and let it rest for about 10 minutes . After that time, remove it from the mold and let it cool on a tray or on the baking paper if you had lined the mold with it.