1Preheat your oven to 350°F (175°C) and grease a 9x5 inch loaf pan.
In a large bowl, cream together the butter and brown sugar until light and fluffy.
Mash the ripe bananas in a separate bowl and then add them to the butter and sugar mixture. Mix well.
Beat in the eggs one at a time, ensuring each is fully incorporated before adding the next.
Stir in the vanilla extract.
In another bowl, whisk together the all-purpose flour, baking powder, and cinnamon.
Gradually add the dry ingredients to the wet ingredients, mixing until just combined.
Fold in the chopped walnuts.
Pour the batter into the prepared loaf pan and smooth the top with a spatula.
Bake in the preheated oven for 60-70 minutes, or until a toothpick inserted into the center comes out clean.
Allow the cake to cool in the pan for about 10 minutes, then turn it out onto a wire rack to cool completely before serving.