Step 1
Preheat the oven to 165C fan-forced (185C conventional). Prepare a Swiss roll tin (30cm x 45cm x 3cm) by lining it with baking paper.
Step 2
In the bowl of a stand mixer, begin whisking the egg whites until foamy then slowly add 40g of the caster sugar. You’re aiming for a meringue with glossy medium peaks and enough structure to fold into the yolk batter without deflating too much, but not dry and overbeaten.
Step 3
In a separate bowl, combine the yolks, the remaining 40g caster sugar, the milk and the oil, and whisk to combine. Sift over the plain flour and cocoa powder and whisk until smooth.
Step 4
Fold half the meringue mix through the egg-yolk mixture, then fold through the rest. Once combined, spread the sponge mixture evenly onto the prepared tin, then place the tin in the oven and bake for 15-17 minutes.
Step 5
While the cake is baking, place a clean tea towel on the bench and dust liberally with cocoa. This will prevent the cake sticking to the tea towel. Once baked, turn the cake out onto the tea towel and rolling up in the towel gently but tightly. Allow it to sit, rolled up, until completely cooled. (Keeping it wrapped in the tea towel helps the cake hold its shape and cool evenly without drying out.)
Step 6
For the creme chantilly, combine all the ingredients in a medium bowl and whisk until stiff peaks form.
Step 7
To assemble, gently unroll the sponge, spread with an even layer of the creme chantilly, leaving 3cm at one end of the cake without filling. Gently roll the sponge up again towards the end without cream, taking care not to press out all the filling.
Step 8
Put the cake in the fridge for a couple of hours to allow the cream to set up. This will allow you to cut beautifully neat slices. I like to dust the top of the cake with extra cocoa powder before serving.
