Preheat your oven to 180°C (gas mark 4, 350°F) and line a loaf tin with parchment paper.
Place butter and light brown sugar into a large mixing bowl and mix together until light and fluffy.
Add eggs, 2 mashed bananas and mix until evenly distributed.
Pour flour, cinnamon and two thirds of the chocolate chunks into the mixing bowl. Mix together until a cake batter has formed.
Spoon half of the banana cake mixture into a lined loaf tin.
Melt Biscoff in the microwave for a few second, you’ll want it runny but not hot. Pour the melted Biscoff spread on top of the banana cake mixture and swirl with a skewer.
Pour the remaining cake mixture into the loaf tin and swirl again using a skewer. Sprinkle the remaining chocolate chunks, slice the remaining banana in two and place it on top of the cake mixture.
Bake in the oven for 60 to 70 minutes. After 30 minutes if the cake is browning too quickly, cover it with foil to stop it browning.
Leave the Biscoff and banana cake to cool for 15 minutes before removing the cake from the loaf tin. Then leave to cool down completely.