Preheat the oven to 356°F/180°C regular oven or 320°F/160°C fan-bake. Grease or line an 8.5x4.5inch (21x11cm) loaf pan with parchment paper.
Melt the butter and let it cool slightly. 100 g butter
In a large bowl, mash the bananas with a fork, then stir in the butter. Add in the brown sugar, eggs, sourdough starter and vanilla, and stir it well together until all combined. 240 g bananas, 2 large eggs, 150 g soft brown sugar, 100 g sourdough discard starter, 1 tsp vanilla extract
In a separate bowl, mix together the flour, baking soda and salt.250 g all-purpose flour, 1 tsp baking soda, 1/2 tsp salt
Tip the dry ingredients into the wet ingredients and fold them together until well combined but not overmixed. Stir through the chocolate chips. 170 g chocolate chips
Spoon the mixture into the prepared loaf tin and bake for approximately 50-60 minutes until a skewer inserted into the loaf comes out clean.
Remove the baked banana bread from the tin and let it cool for 20 minutes before slicing.