Prepare the pan: line a 8-inch (20cm) square baking pan with parchment paper and set aside.
Preheat oven to 325F (160c).
Peel the bananas, place them in a large bowl, then, mash them using a fork. Add egg and whisk until combined. Add peanut butter, ground almonds, maple syrup, cinnamon (optional), baking soda and salt. Miz until combined.
Pour the batter into prepared pan.
Bake for 25-30 minutes or until toothpick comes out clean.
Allow to cool for 5-10 minutes in the pan, the release from the pan and allow to cool completely.