Preheat the oven to 175°C (347°F).
Mash the bananas with a fork.
In a bowl, mix the mashed banana, sugar, melted butter, and egg together.
Sift flour, baking powder, and salt, then add to the batter and mix.
Chop the walnuts finely and add to the batter, then mix well.
Pour the batter into a pound cake pan lined with parchment paper.
Bake in the oven at 175°C (347°F) for 45-50 minutes, then let cool and it's ready.