This is a cake you can get creative with. You can fill it with anything. I had leftover whipping cream and dulce de leche (my husband thought it prudent to buy a kilo of it at Costco). But whipped cream and jam, nutella, etc they all work. You can also frost the top too if desired.
Prepare a 1/2 sheet pan by spraying with Pam, lining it with parchment paper, and spraying again
To make the cake batter whisk together 1/3 cup of cornstarch, 1/3 of a cup of cake flour and 2 tb of cocoa powder
Separate 5 eggs
Whip the yolks with 3 tb of granulated sugar for a few mins and then add 1 teaspoon of vanilla
Whip the whites and slowly add 1/3 of a cup of sugar halfway through
Then fold together the flour, egg whites, and yolk. Add 1/2 of the whitesto the yolks and fold in, then 1/2 of the flour and fold in and then repeat.
Pour into pan and spread it out trying not to deflate it as the rise depends on the whipped eggs.
Bake at 375 for 6-8 mins and loosen the edges with a knife when it is done
Line a cutting board with plastic wrap and sprinkle on some cocoa powder and then flip the cake out onto the cutting board and remove the parchment paper
Let it cool while you make the filling
Whip 1/2 a cup of cream with a 1/2 tsp of vanilla until it is soft but not clumpy (which would be butter)
Spread the cake with about 1/2 a cup of ducle de leche and the whipped cream
Then roll it up using the plastic wrap to help
Then cut off the edges and dust with cocoa powder