Spray the inside of a 6-inch round cake pan with cooking spray, then line it with a single large sheet of parchment paper that completely covers the interior and extends slightly above the edges of the pan. Press and crease the parchment as needed to adhere it to the pan's interior. It's fine if the parchment paper appears wrinkled and uneven around the edges, as this is intended for a rustic-looking cake, meaning the edges won't be perfectly round.

In a large mixing bowl, combine the yogurt and eggs, whisking until the eggs are fully incorporated. If you are adding sugar, mix it in at this stage. Then add the cornstarch and whisk until the batter is smooth. Pour the batter into the prepared baking pan.

For air fryer cooking, preheat the air fryer to 320°F (160°C) and bake for approximately 20-23 minutes. The cake should rise, and the batter should not jiggle or appear liquidy, with a caramelized surface. The cake may deflate slightly upon removal but should not shrink excessively. For oven baking, preheat the oven to 350°F (177°C) and bake for about 70-75 minutes, or until the cake is puffed, the batter is firm, and the surface has caramelized. Once taken out of the oven, the cake will start to deflate and may wrinkle.

Allow the cake to cool at room temperature for about 30 minutes before transferring it to the fridge for at least 2 hours before serving. I typically prepare mine the night before and let it chill overnight in the fridge, as this helps enhance the flavors. Take the cake out of the fridge about 15-30 minutes before serving to allow it to return to room temperature. If desired, drizzle with honey or another sweetener when serving.