Preheat your oven to 350°F (175°C) and prepare a 9-inch round cake pan with cooking spray or parchment paper.

In a large mixing bowl, whip the egg whites at medium speed until soft peaks form, about 3-4 minutes. Add cream of tartar if desired.

In another bowl, whisk together the plain yogurt, granulated sugar, and egg yolks until smooth, about 2-3 minutes.

Sift the all-purpose flour, baking powder, baking soda, and salt over the yogurt mixture and gently fold until just combined.

Carefully fold in the whipped egg whites into the batter in three batches, maintaining their volume.

Pour the batter into the prepared cake pan and bake for 25-35 minutes, until golden brown and a toothpick comes out clean.

Let the cake cool in the pan for about 10 minutes, then transfer to a wire rack to cool completely.