01 - Preheat the oven to 325°F. Line the bottom of an 8-inch round cake pan with parchment paper, leaving the sides ungreased to help the cake climb and rise properly.
02 - In a medium bowl, whisk together the flour, sugar, baking powder, and salt until well blended and evenly distributed.
03 - In a large bowl, whisk the egg yolks, Greek yogurt, vegetable oil, vanilla extract, and lemon zest until the mixture is smooth and homogeneous.
04 - Add the dry ingredients to the wet mixture and stir just until combined, being careful not to overmix. The batter will be thick.
05 - Using a clean bowl and beaters, beat the egg whites with an electric mixer until stiff peaks form. The whites should stand upright when the beaters are lifted.
06 - Gently fold one-third of the beaten egg whites into the batter to lighten the base. Then carefully fold in the remaining egg whites, using a rubber spatula and lifting motion to preserve as much air as possible.
07 - Transfer the batter to the prepared cake pan and smooth the top with a spatula. Tap the pan gently on the counter to release any large air bubbles.
08 - Bake for 35 to 40 minutes, or until the top is golden brown and a toothpick inserted into the center comes out clean.
09 - Let the cake cool in the pan for 10 minutes. Run a thin knife around the edges to release, then invert onto a wire rack. Allow to cool completely before serving.
10 - Dust the cooled cake generously with powdered sugar before serving. For enhanced presentation, slice with a serrated knife and serve plain or with fresh berries and whipped cream.