Whisk the egg yolks in a bowl at maximum speed for five minutes (until the yolks become pale, thick and creamy).
In a second bowl, beat the butter and sugar together until creamy.
Add the lemon zest and vanilla extract and mix well. Add the egg yolks and beat well
Adding flour and cornstarch and blend again.
Beat the egg whites until stiff. Fold a third of the egg whites into the batter to loosen it.
Then, gently fold in the rest of the egg whites.
Preheat the oven grill. Grease a 20cm mold with oil and line with parchment paper.

Pour part of the batter (1/20th) into the bottom of the pan and spread it evenly across the bottom using the back of a spoon. Bake for approximately 2 minutes until a nice pale color is obtained. Remove the mold, add a second thin layer, spread it evenly and return to the oven, this time for approximately 3 minutes, until you get a nice dark color.
Repeat for the next 18 layers, the more the layers overlap, the more the cooking time decreases because the dough gets closer to the grill, so watch it closely.
After the dough is used up, remove from the oven and let cool for 5 minutes. Unmold and place on a wire rack.
Spread the jam on the surface and around the edge of the cake.
Prepare the chocolate icing:
Melt the butter, syrup, and vanilla in a saucepan and bring to a boil.
Remove from the heat, and add chocolate until it melts. Let cool until thick.
Pour the chocolate frosting over the cake and spread with a spatula.
Preparing vanilla frosting:
In a bowl, pour the icing sugar, vanilla and milk. Mix well.
Place the frosting in a freezer bag, finely cut the end and make grids.