Step 1

Preheat the oven to 175°C. Spray a 1.5L loaf pan with non-stick spray. Sugar the inside of the pan with 1/4 cup of the demerara sugar (or regular sugar if you don’t have demerara), tapping out any excess.

Step 2

In a medium bowl, whisk the flour, cocoa powder, baking powder and salt together; set aside.

Step 3

Using a stand mixer fitted with the paddle attachment, beat the butter, raw sugar, light-brown sugar and vanilla on high speed until the mixture is super light and fluffy, 3-5 minutes. Using a spatula, scrape down the sides of the bowl and add the egg. Beat until well combined and the mixture returns to that previously light, fluffy state, about 2 minutes. With the mixer on low, slowly add dry ingredients and beat just to blend. Using a spatula, fold in the mashed bananas, followed by the mascarpone, mixing just to blend.

Step 4

Spoon the batter into the prepared loaf pan, smoothing the top. Place the banana halves, cut-side up, on top of the batter. Sprinkle with the remaining 1/4 cup demerara sugar and bake until the sides start to pull away and the cake is baked through in the centre (it’s a very dense, moist cake, but it should still spring back slightly when pressed in the centre), 90-100 minutes.

Step 5

Let cool completely before slicing.