Preheat oven to 350°F. Spray the interior of a 6-inch round springform pan with cooking spray and then line it with a large sheet of parchment paper so that it completely covers the interior of the cake pan and comes up slightly above the pan. Press and crease the parchment paper as needed so that it sticks to the interior edges. You want to use a single sheet of parchment paper. It is okay that the parchment paper will be wrinkled and uneven around the edges. Just try your best to press it flatly against the sides and bottom. This is supposed to be a rustic-looking cake so the cake edges will not be perfectly round.

In a large bowl add yogurt. If you are using sugar (see notes), add it now and whisk it in. Add eggs, one at a time, whisking after each addition until the egg is completely blended into the yogurt. When you are finished, you should have a smooth batter.

Sift the cornstarch into the batter. You can do this using a mesh strainer. Whisk the cornstarch into the batter, until no cornstarch lumps remain.

Pour batter into prepared baking pan. Bake for about 1 hour or until cake is puffed up, no longer wet on top and the surfaces has a caramelized appearance. When the cake comes out of the oven it will begin to deflate and wrinkle. Let cake cool at room temperature for about 30 minutes and then place into fridge for at least 2 hours before serving. Letting the cake sit in the fridge will help develop the flavors. If you try to eat the cake right away, it will be a little eggy and not sweet. Remove cake from the fridge about 15 minutes before serving so that the came can come back to room temperature, which will make it less firm and more creamy.