Preheat the Oven: Start by preheating your oven to 180°C (350°F) and line a baking tray with parchment paper.
Make the Sponge Cake:
In a large mixing bowl, whisk the eggs and sugar until thick and pale (about 5-7 minutes).
Sift together the flour, baking powder, and salt; gently fold it into the egg mixture, ensuring you deflate the air as little as possible.
Bake the Cake: Pour the batter into the prepared tray, smoothing the top. Bake for about 10-12 minutes or until lightly golden and springy to the touch.
Prepare the Caramel: While the cake is baking, make the caramel by melting the sugar in a saucepan over medium heat until it turns golden. Slowly whisk in the heavy cream and stir until smooth. Add mashed bananas and vanilla extract, mixing well. Allow to cool slightly.
Assemble the Roulade: Once the cake is baked, turn it out onto a clean kitchen towel dusted with icing sugar. Remove the parchment paper and spread the banana caramel filling evenly over the cake. Roll it up tightly using the towel to help guide you.
Chill and Serve: Wrap the roulade in plastic wrap and chill for at least 30 minutes before serving. Slice it up and serve with extra caramel drizzled on top if desired!