Finely chop the chocolate and place into a medium heat-proof bowl.
Heat the cream and butter in a small pot until the butter has melted and the cream is gently steaming.
Pour this over the chocolate in the bowl. Let sit for 5 minutes then gently stir until all the chocolate has melted.
Let this mixture cool at room temperature for 45-60 minutes, stirring occasionally, until thickened but still pipeable.
Prepare the pan:
Preheat the oven to 350 degrees F.
Use the 2 tablespoons of softened butter and a pastry brush to coat a 12-cup bundt pan very well. Add the cocoa powder to the the pan, tilting and tapping the pan to coat as much of the inside as possible. Tap out any excess cocoa powder.
For the cake:
In a large bowl, beat the butter, granulated sugar and dark brown sugar together until smooth. Beat in the eggs one at a time until smooth. Add the salt, vanilla, baking powder, vegetable oil and mashed banana and stir together until well-combined.
Add the flour and cocoa powder to the bowl and mix until just combined.
Scoop 3 cups of the cake batter into the prepared bundt pan. Spread out into an even layer.
Transfer the thickened, cooled fudge filling to a piping bag. Pipe the fudge filling in a thick ring all the way around in the centre of the batter.
Cover the fudge filling with the remaining cake batter and spread out evenly in the pan.
Bake for 35-40 minutes. The cake will look risen and dry on top. You won’t be able to test this cake with a toothpick as the centre will still be gooey when the cake is finished baking, so you must ensure your oven is at the correct temperature.
Remove the cake from the oven and let cool for 20 minutes in the pan. Loosen the edges of the cake with a small spatula or butter knife, flip the cake out onto a wire rack and leave to cool completely.
For the frosting:
In a small bowl, stir together the powdered sugar, cocoa powder and milk until smooth.
Spoon over the top of the cooled cake, letting it drip down the sides of the cake. Top with the dried banana chips and leave the icing to set for a few minutes before cutting into the cake.
12-cup Nordicware Classic Bundt Pan (aka Anniverary Bundt Pan). Buy it now on Amazon: https://www.amazon.com/Nordic-Ware-12-Cup-Bundt-Pan/dp/B0000CFLM2.