Preheat oven to 180C. Line a deep baking tray with baking paper and set aside. 

In a large bowl, or using your stand mixer, combine the melted butter and brown sugar until fully incorporated. Add vanilla essence and egg, and mix until fully incorporated. 

Add plain four and cinnamon, and stir until combined. Next stir in the mashed banana and chocolate chips until just combined. 

Pour the mixture into the prepared pan and place in the oven. Bake for 25-30 minutes, or until the top is set and slightly golden. 

Remove from the oven and cool for at least 10 minutes before cutting. Cut into even pieces and serve immediately, or keep in an airtight container for up to a week.