• Pre-heat oven to 370℉/180℃. Line an 8x8" baking pan.
• 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. Alternatively, set up a double boiler. Do this by placing a heatproof bowl over a small pot of simmering water. Add the chocolate to the heatproof bowl and stir until melted. 
• In a large mixing bowl, whisk together melted butter, bananas and both sugars until fully combined (3-5 minutes) A few lumps from the bananas is fine. Add in the eggs and whisk again. Finally, add the melted chocolate and whisk to combine.
• Add the flour, salt and cocoa powder. Fold gently with a rubber spatula or wooden spoon until everything is combined - you can't really overmix a brownie, so don't panic!
• Pour the batter into the lined pan. Bake approx 25-28 minutes. Remove and let cool before the next step.

For the Peanut Butter Frosting

• Add the butter and peanut butter to a bowl/the bowl of a stand mixer. Whisk on high until combined and fluffy. Add half of the powdered sugar and mix until combined. Then, add the remaining powdered sugar. It should be thick!
• Spread over the cooled brownies. Put the brownies in the refrigerator while working the next step.

For the Ganache

• Chop the chocolate up into small pieces if using block chocolate (chocolate chips are fine too). Place the chocolate in a heatproof bowl/jug.
• Heat the cream over a medium heat in a small saucepan. Once it has started simmering, pour it over the chocolate. Leave for 2 minutes, then whisk to create a thick, glossy chocolate ganache. Pour over the brownies.
• Optional: decorate with peanut butter candies/chocolate - do this while the ganache is still wet so that they stick in place! Let cool in the refrigerator (and keep stored there). Slice and serve when the ganache is set (whenever it can be sliced!).