Preheat the oven to gas mark 6 (400°F/200°C). Grease and line a Swiss roll tin or a 25x35cm rectangle tin with greaseproof paper that hangs over the edges.
Whisk together the eggs, caster sugar, and light brown sugar until the mixture is thick and light in color (about 5 minutes with an electric whisk).
Gently fold in the plain flour and baking powder until combined. Pour the mixture into the lined tin, tilting it so the batter reaches all corners evenly.
Bake for 10 minutes or until golden brown and the sponge springs back when touched
Sprinkle caster sugar on a sheet of greaseproof paper and flip the baked sponge onto it. Roll the sponge tightly with the paper and set it aside to cool.
Prepare the fillings by whipping the double cream until soft peaks form. Chop the banana into small chunks and set aside.
Carefully unroll the cooled sponge and peel back the inner layer of greaseproof paper. Spread a layer of caramel, followed by whipped cream, and sprinkle the banana chunks.
Roll the sponge back into a spiral using the greaseproof paper to guide it. Drizzle the reserved caramel and melted dark chocolate over the top of the roulade. Serve and enjoy!