Mix together the black beans, oats, almond butter, honey, egg, Greek yogurt, and baking powder in a large bowl until well combined. The mixture should be smooth and relatively free of lumps. (Colour: the mixture will be a deep brown, with a subtle sheen from the almond butter.)

Add in the chopped dark chocolate, walnuts, and salt. Mix until the ingredients are evenly distributed throughout the batter. (Texture: the mixture will start to thicken and develop a crumbly texture from the oats and chocolate.)

Stir in the vanilla extract and chopped fresh mint leaves (if using). (Smell: the mixture will start to emit a sweet, malty aroma from the almond butter and honey.)

Press the mixture into a lined or greased 8-inch square baking pan. (Sound: the mixture will make a satisfying 'thud' as it settles into the pan.)

Bake at 180°C (350°F) for 25-30 minutes, or until a toothpick inserted into the centre of the brownies comes out clean. (Colour: the edges will be lightly golden, while the centre will be still slightly soft and underbaked.)

Store the brownies in an airtight container in the fridge for up to 5 days. (Colour: the brownies will retain their colour and remain moist, even after storing.)

Reheat the brownies in the microwave or oven before serving. (Sound: the brownies will make a satisfying 'splat' as they reheat, releasing a fragrant aroma into the air.)