For key visual process photos, refer to the body of the blog post.

Make the cake:

• Preheat the oven to 325°F/163°C.
• Prepare a 9" by 13" baking sheet with parchment paper. Have another large piece of parchment paper ready for later use.
• In a bowl, whisk together the oil, milk, 20g granulated sugar, and vanilla extract.
• Sift the flour and cornstarch into the wet ingredients.
• In a clean stand mixer bowl fitted with a whisk, add in 4 egg whites and beat on low-medium speed until foamy.
• Gradually increase the mixer speed and add in the cream of tartar (or lemon juice). When you begin to see lots of bubbles, add in the 35g granulated sugar gradually and continue beating until egg whites reach soft peaks. (When you remove the whisk, the egg whites will have the shape similar to a bird's beak).
• Transfer about 1 C of the whipped egg whites to the flour mixture and fold it in. Once lightened, add the remaining egg whites in ⅓rd additions to the flour mixture to incorporate. Be careful not to overmix.
• Transfer the cake batter to the prepared baking sheet and smooth out the top with an offset spatula. Drop the pan from a height of about 1 foot to release any trapped air bubbles. You may need to drop it a few times until no bubbles appear on the surface.
• Bake at 325°F/163°C for 15-16 mins, or until the cake is springy and firm to the touch.
• Remove cake from the oven and drop the pan from a height of about 1 foot to prevent the cake from shrinkage.
• Cool the cake on a cooling rack for about 10-15 minutes, until slightly warm to the touch.

Make the whipped cream:

• Add the cold heavy whipping cream, vanilla extract and powdered sugar to a large, chilled bowl.
• Use a balloon whisk and whip until the cream is light and airy.

Assemble the cake:

• Peel the parchment paper off the cake.
• Transfer the almost completely cooled cake onto a clean piece of parchment paper.

  Note: You may need to carefully flip the cake twice for the browned side (skin side) to be on top, which will roll with the white side facing outward.
• Spread the whipped cream onto the entire surface of the cake.
• Carefully roll the cake with the cream. (You can roll it lengthwise or widthwise, your choice).
• Wrap the cake up with the parchment paper and twist the ends to secure. Place cake onto a large plate and wrap with plastic wrap to seal.
• Set into the fridge to chill for at least 4 hours.
• Use a clean serrated knife to trim off the ends.
• Garnish cake with whipped cream and berries, and serve cake in slices.