Preheat the oven to 350°F (175°C). Line the bottom and sides of a 6-inch (15 cm) springform pan with parchment paper and set aside.
In a large bowl, combine the plain Greek yogurt, eggs, and sugar. Whisk until the mixture is smooth and uniform.
Add the cornstarch to the yogurt mixture and whisk thoroughly until no lumps remain and the batter is smooth.
Pour the batter into the prepared springform pan and gently tap the pan on the counter to release any air bubbles.
Bake for 1 hour, until the center is puffed and the edges are lightly browned.
Remove the cake from the oven and let it cool at room temperature for 30 minutes; the center will deflate as it cools.
Transfer the cake to the refrigerator and chill for at least 2 hours, or until firm.
When chilled and firm, unmold the cake. Let it sit at room temperature for 15 minutes before slicing and serving.
Optional: dust with powdered sugar or serve with fresh berries if desired.
