Preheat the oven to 170°C fan / 375°F / Gas 5.
Line a 20 x 35cm (9 x 14 inch) baking tray with baking/parchment paper.
Using a stand mixer or electric hand mixer, whisk the eggs and sugar in a medium bowl. Continue whisking for about 3-4 minutes until they are pale and fluffy and double in size.
Next, add the milk, oil, flour, cornflour salt, baking powder, and gently incorporate them all by folding the batter with a rubber spatula or spoon.
Just fold the ingredients enough that there are no lumps of flour. Be careful not to overmix or the batter or it will lose all the air we incorporated at the beginning while whisking the eggs.
The cake batter may seem very liquid, but do not worry. Pour the batter into the prepared pan and smooth the batter into an even layer using the a spatula.
Baking: Place the tray on the middle shelf and bake for 10-12 minutes until the cake is light and golden brown or a knife poked into the middle comes out clean.
Remove the cake from the oven and roll the cake up into a roll. Be careful not to burn yourself. Let it sit rolled up for 30 seconds then unroll it and leave it to cool completely. (approx. 20 minutes)
Filling: Whisk the cream with the mascarpone until it forms soft peaks and then add the icing sugar.
Spread jam onto the sponge in a nice even layer.
Then spread over the mascarpone cream.
Finally, roll it up nice and tight.
Place the swiss roll into the fridge for 30 minutes.
Then dust with icing sugar and serve.