Step 1: Prepare the Chocolate Sponge Cake

Preheat your oven to 350°F (175°C). Line a jelly roll pan with parchment paper, ensuring it fits snugly.

In a large mixing bowl, beat the eggs and sugar with an electric mixer on high speed for about 5 minutes, until thick and pale.

Sift the flour, cocoa powder, baking powder, and salt together. Gently fold the dry ingredients into the egg mixture in batches. Add the vanilla extract and mix until just combined.

Pour the batter into the prepared pan and spread evenly. Bake for 10–12 minutes, or until the cake springs back when lightly pressed.

Step 2: Roll the Cake

While the cake is still warm, turn it out onto a clean kitchen towel dusted with powdered sugar. Carefully peel off the parchment paper.

Starting from the short end, gently roll the cake with the towel into a log shape. Let it cool completely, about 30 minutes.

Step 3: Make the Banana Cream Filling

In a chilled mixing bowl, beat the heavy cream, powdered sugar, and vanilla extract until stiff peaks form.

Gently fold in the mashed bananas. Chill the filling until ready to use.

Step 4: Assemble the Roll

Unroll the cooled cake and spread the banana cream filling evenly across the surface, leaving a small border around the edges.

Carefully re-roll the cake (without the towel) and transfer it to a serving platter.

Step 5: Prepare the Chocolate Ganache

Heat the heavy cream in a microwave-safe bowl until hot but not boiling. Pour over the chocolate chips and let sit for 2 minutes. Stir until smooth and glossy.

Pour the ganache over the cake roll, spreading evenly with an offset spatula.