In a bowl, mix together the butter and sugar until smooth.
Slowly add in the beaten eggs and mix in until combined.
Add in the flour, baking powder and ground cinnamon and mix.
Finally, stir in the mashed bananas.
Transfer the mixture to the loaf tin and bake for 45 minutes. Check on it at around the 30 minute mark - if the outside seems to be browning up too quickly you may need to loosely cover it with foil for the final 15 minutes of cooking time.
Check the banana bread is cooked through by inserting a skewer in the middle, if it comes out clean it is ready.
Leave the banana bread to cool for 10 minutes in the tin before transferring to a wire rack to cool some more before slicing and serving.