01 - Preheat oven to 325°F. Line the bottom of an 8-inch round cake pan with parchment paper. Leave the sides ungreased to help the cake climb properly.
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, about 3 minutes. Add oil, yogurt, vanilla extract, and lemon zest. Mix until smooth and fully incorporated.
04 - Gently fold the dry ingredients into the wet mixture using a spatula. Mix until just combined—some small lumps are acceptable. Do not overmix.
05 - In a clean bowl, 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 - Fold one-third of the beaten egg whites into the batter to lighten it. Gently fold in the remaining whites in two more additions using a spatula. Work carefully to maintain airiness.
07 - Transfer batter to the prepared pan. Smooth the top evenly with a spatula. Tap the pan gently on the counter once to release any large air bubbles.
08 - Bake for 40-45 minutes until the cake is set and golden. A toothpick inserted in the center should emerge clean. Avoid opening the oven during the first 30 minutes.
09 - Let the cake cool in the pan for 10 minutes. Run a thin knife around the edge to loosen. Invert onto a wire rack, peel off the parchment, and cool completely before serving.
10 - Dust generously with powdered sugar just before serving. Accompany with fresh berries or fruit if desired. The cake can be served at room temperature or chilled.