Add the sugar to the eggs and beat it until it's smooth and fluffy. I've used my kitchen aid, so I didn't separate the egg whites of the yolk. The texture has to be fluffy and creamy.
Add the lemon zest and the vanilla extract.
Sift the flour and the cornstarch in a bowl with the baking powder. Slowly and gently start to fold the flour into the eggs.
Take the 10-inch cake pan, lined with parchment paper and pour the dough in it. I've used 2 baking sheets, so I've divided the dough in 2. If you have only 1 baking sheet - no worry. It just takes a longer time to bake.
Put it in the oven and bake it for 30-35 minutes make sure you check in the middle making sure it's done. If you using 1 baking pan increase the time with 5 -10 minutes and if you see that it's starting to getting brown on the top just cover it with a foil.