Preheat your oven to 350°F (175°C) and grease a 9-inch cake pan. Line with parchment paper.

In a large mixing bowl, combine yogurt, sugar, and eggs. Blend until smooth and creamy.

Gradually sift in flour, baking powder, and salt. Gently fold until just combined.

Beat egg whites until soft peaks form. Add cream of tartar if using. Fold into batter in three additions.

Pour batter into prepared pan and bake for 25-35 minutes. Check for a golden top and clean toothpick.

Let cake cool in the pan for 10 minutes before transferring to a wire rack to cool completely.