Pre-heat your oven to 370℉/180℃. Line an 8" Square Pan with greaseproof paper.
In a small bowl, break up the dark chocolate and melt in the microwave in 20 second intervals, stirring in between to make sure it doesn't burn.
In a large mixing bowl or the bowl of a stand mixer, whisk together the melted butter, bananas and both sugars. Go for a solid 3-5minutes so it is totally combined. Add in the eggs and combine again.
Now, add the melted dark chocolate slowly (check it first, to make sure it isn't so hot that it will cook the eggs) and combine once again.
Add the flour, cocoa powder and the chopped chocolate. Fold gently into the wet mixture with a rubber spatula or wooden spoon until just combined.
Pour the batter into the lined pan and bake for 30-35 minutes. Let cool on a wire rack before making the glaze.
Make the glaze: combine the melted butter, maple syrup and icing sugar with a whisk until smooth. Leave about 10 minutes before pouring over, then let set in the fridge before slicing and serving!