Heat oven to 180°C / 350°F / Gas 4. Line a half sheet pan (standard oven sized, rimmed baking tray approx 46 x 33 cm) with baking paper and grease well with butter.

Using an electric mixer beat eggs, sugar and vanilla together until very light and fluffy, at least 5 minutes, then drizzle in the oil, beating continuously until incorporated.

In a separate bowl, whisk together the flour, cocoa, baking powder and salt. Gently, but thoroughly fold the dry ingredients into the beaten egg mixture, ensuring it is well combined but keeping as much air in the mixture as possible.

Spread evenly over the prepared baking tray, then bake in the preheated oven for 15-18 minutes until risen. Meanwhile, lay a clean tea towel on the benchtop and sprinkle generously with the additional 2 tablespoons of sugar. When the cake is cooked, remove from the oven, allow to cool for 2-3 minutes, then invert the warm cake onto the sugared towel - be brave!

Carefully peel off the baking paper, turn the paper over and replace, then starting from one of the short sides, roll up tightly using the paper and towel to assist. Allow to cool at least 15-20 minutes before filling.

While the cake is cooling make the decoration and filling. Melt the chocolate in a heatproof bowl set over simmering water. Spread over one side of a piece of baking paper, fold the baking paper in half then roll into a tube, securing with a rubber band. Place in the freezer until needed. Wash and drain the berries well, hulling and chopping the strawberries.

Whip the cream to soft peaks, drizzling in the icing sugar and cornflour while the beaters are on low speed, then increase the speed to high and whip to stiff peaks.

Unroll the sponge, spread with cream, leaving a 2cm border at the end which will be the seam. Reserve 2-3 tablespoons cream for decoration. Scatter over some of the berries, then re-roll tightly. Transfer to a serving platter or plate and chill until ready to serve, at least an hour or two to allow the cake to stabilise.

When you are ready to serve, trim the ends, spread the reserved cream down the middle of the roulade. Top with the berries, then unroll the chocolate from the freezer. It will break into large shards which you can place amongst the berries. Surround the roulade with any remaining berries and serve immediately.