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 properly.
02 - In a medium bowl, whisk together the flour, sugar, baking powder, and salt until well incorporated.
03 - In a large bowl, whisk the egg yolks, Greek yogurt, vegetable oil, vanilla extract, and lemon zest until completely smooth and emulsified.
04 - Add the dry ingredients to the wet mixture and stir just until combined. Do not overmix to maintain a tender crumb.
05 - Using a clean bowl and electric mixer, beat the egg whites until stiff peaks form. This is crucial for the cake's airy texture.
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, retaining as much air as possible for maximum fluffiness.
07 - Pour the batter into the prepared cake pan and smooth the top with a spatula.
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, then run a knife around the edges and invert onto a wire rack. Allow to cool completely.
10 - Dust generously with powdered sugar before serving, if desired. Slice and enjoy as a light dessert or teatime treat.