Preheat your oven to 180 degrees and line the base of a DEEP 20cm round cake tin.
Place the butter and sugar together in the bowl of an electric mixture and beat until they mixture is light and fluffy.
Add the eggs to the creamed butter and sugar one at a time, make sure you beat each egg in well before the next addition.
Remove the bowl for the electric mixer stand and sift in the flour, bicarbonate of soda and cinnamon.
Add the mashed bananas and carefully fold through until the mixture has just combined.
Spoon the cake mixture into a lined and deep 20cm cake pan (or a 22cm ring tin) and bake for 50 minutes (if cooking in a round tin) or 35 minutes if baking in a ring tin or until the cake is cooked when tested with a skewer