Spray the inside of a 6-inch round cake pan with cooking spray, then line the pan with a single large sheet of parchment paper, ensuring it covers the entire interior and rises slightly above the edges of the pan. Press and crease the parchment paper as needed so it adheres to the pan. It’s fine if the parchment paper appears wrinkled or uneven around the edges, as this is a rustic-style cake, and the edges will not be perfectly round.

In a large mixing bowl, combine the yogurt and eggs. Whisk until the eggs are fully incorporated. If adding sugar, mix it in now. Add the cornstarch and whisk until the batter is smooth. Pour the batter into the prepared cake pan.

For air fryer cooking: Preheat the air fryer to 320°F (160°C) and bake for about 20-23 minutes. The cake should be puffed up, the batter should no longer be jiggly or liquid, and the surface should have a caramelized appearance. The cake may deflate slightly when removed but shouldn’t shrink too much.

For oven baking: Preheat the oven to 350°F (177°C) and bake for about 70-75 minutes, or until the cake is puffed up, the batter is set, and the surface is caramelized. When removed from the oven, the cake will begin to deflate and may wrinkle.

Allow the cake to cool at room temperature for about 30 minutes, then transfer it to the fridge for at least 2 hours before serving. For the best flavor, I recommend making the cake the night before and letting it chill overnight in the fridge. Remove the cake from the fridge 15-30 minutes before serving to bring it to room temperature. If desired, drizzle with honey or another sweetener before serving.