• Preheat the oven to 350°F/180°C with a rack in the center.  Grease a 15x10x1 inch jelly roll pan with oil or cooking spray and line it with a sheet of parchment paper. Greasing the tray first helps the parchment stick and keeps the bottom surface flat
• Separate 4 large eggs. Place the egg yolks in a small bowl and set them aside. Add the egg whites to the large stand mixer bowl and turn it on, whisking at high speed until the mixture becomes foamy.
• Gradually add in half of the sugar while continuing to whisk until the egg whites form medium-stiff peaks. The peaks should hold their shape well, but if you lift the beater from the mixture, they will flop to the side.
• Transfer the whipped egg whites to a clean mixing bowl and set them aside.
• Add the egg yolks, remaining sugar, oil, vanilla, and salt using the same stand mixer bowl. There's no need to clean the bowl first.
• Whisk the egg yolks on high speed for approximately 4-5 minutes until they triple in volume and become thick and pale. The light yellow egg mixture should drop thick, flowing ribbons back into the bowl when lifting the beater out of the mixture.
• Using a rubber spatula, fold a third of the egg whites into the beaten yolk mixture, not deflating the air bubbles in the egg whites.
• Gently bring the spatula through the middle of the mixture, up the side, and fold it over the top. You can rotate the bowl as you do this. Repeat this process two more times with the remaining egg whites.
• Balance a sieve over the bowl of eggs and sieve in roughly half of the flour.
• Using a gentle folding motion, carefully incorporate the flour into the egg mixture, being cautious not to deflate it too much. Repeat this process once more with the remaining flour. The final batter should have a light and airy texture while also being thick.
• Pour the cake batter into a prepared pan and use an offset spatula or dough scraper to carefully spread the batter out into an even layer on the tray.
• It's a very thick and light batter so it won't fill out by itself the way that wet cake batters do. Spread it out to reach the sides of the pan.
• Bake the sponge for around 10-12 minutes until light golden brown on the top and the tip of the cake springs back when gently pressed. While the cake is baking, lay a clean kitchen towel on a workbench, horizontally so the long edge is closest to you. Generously dust it with powdered sugar.
• Once the sponge has finished baking, carefully tip it upside down with the long edge closest to you, onto the towel. Carefully peel off the parchment paper.
• Dust the cake with more powdered sugar, then starting from the short side, roll the cake and the towel up together into a spiral.
• Leave it to cool on a wire rack until it's at room temperature.

The cream filling

• As the cake cools, prepare the whipped mascarpone cream. Combine the mascarpone, powdered sugar, and vanilla extract in a medium bowl. Use a hand mixer or stand mixer with a paddle attachment, starting on low speed, to mix until everything is combined.
• Slowly increase the speed to medium and gradually pour in the heavy cream while continuing to whisk until the mixture becomes thick and holds stiff peaks. Take care not to overbeat it, as it can curdle and separate.

Assembling

• On a clean work surface, carefully unroll the cooled cake.
• Spread over the whipped cream mixture and use an offset spatula to spread it out, leaving a ½ inch border on all sides. Dollop over the lemon curd, then spread it over the cream with an offset spatula.
• Carefully re-roll the lemon roll, without the kitchen towel, back into a spiral. Some thin crust outside the cake may stick to the towel as you roll, but this can be covered with powdered sugar.
• Wrap the kitchen towel around the rolled cake and let the cake chill in the refrigerator for 30-60 minutes.

Serving

• Remove the cake from the refrigerator and cut off the ends of the roll with a serrated knife (about ¼ inch of each end) to neaten them up. Dust with powdered sugar before serving.