01 - Preheat oven to 325°F. Line the bottom of an 8-inch round cake pan with parchment paper, leaving the sides ungreased.
02 - Whisk together flour, cornstarch, baking powder, and salt in a bowl. Set aside for later use.
03 - Whisk egg yolks with 1/2 cup sugar until pale and creamy. Blend in oil, yogurt, vanilla extract, and lemon zest until smooth.
04 - Gently fold the dry ingredients into the wet mixture until just combined. Avoid overmixing to maintain the light texture.
05 - Beat egg whites with an electric mixer on medium speed until soft peaks form. Gradually add remaining 1/4 cup sugar and continue beating until stiff, glossy peaks form.
06 - Lighten the batter by folding in one-third of the beaten egg whites. Gently incorporate the remaining egg whites in two more additions, using a folding motion to preserve air pockets.
07 - Transfer the batter to the prepared pan. Smooth the surface with a spatula, ensuring an even layer.
08 - Bake for 40 to 45 minutes until the cake is set and a toothpick inserted in the center comes out clean.
09 - Let the cake cool in the pan for 10 minutes. Run a knife around the edge, carefully invert onto a wire rack, and remove the parchment paper. Allow to cool completely.
10 - Dust the cooled cake generously with powdered sugar. Serve with fresh berries or fruit if desired.