Preheat your oven to 350°F (175°C) and prepare your baking tin by lining it with parchment paper.

Mash the very ripe bananas in a mixing bowl until completely smooth and creamy.

Melt together the butter and dark chocolate in a heatproof bowl over simmering water or microwave in 30-second intervals.

Stir in the prepared mashed bananas and sugar until well mixed.

Incorporate the eggs one at a time, mixing gently until just combined.

Sift in the plain flour and fold gently until no flour specks remain; do not overmix.

Pour the batter into the prepared baking tin and bake for 25-30 minutes, until edges are set.

Let the brownies cool in the tin for 10-15 minutes before slicing and serving.