Preheat your oven to 160C Fan / 180C and prepare a 2lb loaf tin.
Cream together the light brown sugar and butter until light and fluffy.
Next add your beaten eggs alongside your mashed banana (I tend to just mash mine with a fork!). Either by hand or with a whisk, mix your eggs and banana in until combined. At this stage you'll realise how important it is to have very ripe bananas - if they are underripe it's harder for them to combine.
Add your gluten free flour, sifted cocoa powder and bicarbonate of soda to the bowl and mix briefly just to combine and so that no dry flour can be seen. Fold in your chocolate chips at this point, if using.
Spoon / pour your mixture into a prepared 2lb loaf tin And place in the oven for about an hour.
Check that it's cooked by sticking a skewer into the centre and seeing if it comes out clean. Allow to cool fully.