01 - Preheat oven to 325°F. Line bottom of 8-inch round cake pan with parchment paper. Leave sides ungreased to allow proper rising.
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. Add oil, yogurt, vanilla extract, and lemon zest; mix until smooth and fully incorporated.
04 - Gently fold dry ingredients into wet mixture until just combined. Avoid overmixing to maintain light texture.
05 - In clean bowl, beat egg whites with electric mixer on medium speed until soft peaks form. Gradually add remaining 1/4 cup sugar and beat until stiff, glossy peaks form.
06 - Gently fold one-third of beaten egg whites into batter to lighten. Fold in remaining egg whites in two additions, being careful not to deflate the mixture.
07 - Transfer batter to prepared pan. Smooth top with spatula, ensuring even distribution.
08 - Bake for 40-45 minutes until set and toothpick inserted in center comes out clean. The cake should be golden and spring back when touched.
09 - Let cool in pan for 10 minutes. Run knife around edge, invert onto wire rack, and peel off parchment. Cool completely before serving.
10 - Dust with powdered sugar and accompany with fresh berries if desired. Best enjoyed same day but keeps airtight for 2 days.