In a large bowl, add sugar and salt. Sift together the flour, cocoa powder, baking powder, and baking soda. Stir to combine the dry ingredients well.
In a separate large bowl, mash the ripe bananas with a fork until smooth.
Add the egg, oil, and vanilla extract to the banana. Mix well with a whisk until everything is fully combined and smooth.
Add the dry ingredients to the wet mixture. Stir gently with a spatula until just combined, being careful not to overmix the batter.
Pour in ⅓ the hot simmering water, and mix well. Then pour the rest of the hot water, and mix until the batter is smooth and slightly runny.
Pour the batter into the prepared cake pan with parchment paper.
Bake in a preheated oven at 185°C / 365°F (for a regular oven) or 170°C /338°F (for a fan-assisted oven) for 40-45 minutes, or until a toothpick inserted in the center comes out clean.
After baking, let the cake cool in the pan on a wire rack for 30 minutes. Then, take the cake out of the pan and place it directly on the wire rack to cool completely.
Once the cocoa banana cake has completely cooled, cut the cake into two equal parts.
Place a cake layer on the middle of a cake stand. Add 3 tablespoon of cocoa frosting onto the cake and spread into an even layer.
Top with the second cake layer. Spread the remaining frosting onto the top and sides of the cake. Refrigerate for 30 minutes before slicing to help set the shape.
Notes
Use Very Ripe Bananas: The riper, the better! Bananas with brown spots or fully brown skin add more sweetness and flavor.Mash well: Mash the bananas smoothly to avoid lumps. A fork works, but a blender makes it extra smooth.Don’t Overmix: Stir the wet and dry ingredients just until combined. Overmixing can make the cake dense and tough.Add Hot Water in Stages: Pour hot water gradually to help mix everything evenly and prevent lumps. Hot water also makes the cocoa richer and the cake more moist.Prepare the Pan: Line the cake pan with parchment paper to prevent sticking.Check for Doneness: Insert a toothpick in the center. If it comes out clean or with a few crumbs, it’s done! Avoid overbaking to keep it moist.Slicing Tip: Use a cake cutter to slice the cake layers evenly. Refrigerate the cake for a bit before slicing for cleaner, even cuts.Cool before Frosting: Let the cake cool completely before frosting, or the frosting will melt. You can even chill the cake layers for 30 minutes to firm them up.Frost Evenly: Use an offset spatula to spread the frosting smoothly on the layers and the top.Storage: Store leftover cake in an airtight container at room temperature for 1-2 days or refrigerate for up to 5 days. Let it come to room temperature before serving for the best texture.