01 - Preheat oven to 325°F. Line the bottom of an 8-inch round cake pan with parchment paper. Do not grease the sides.
02 - Whisk together the flour, sugar, baking powder, and salt in a medium bowl until well blended.
03 - Whisk the egg yolks, Greek yogurt, vegetable oil, vanilla extract, and lemon zest in a large bowl until smooth and creamy.
04 - Add the dry ingredients to the wet mixture and stir just until combined. Do not overmix.
05 - In a clean bowl, beat the egg whites with an electric mixer until stiff peaks form.
06 - Gently fold one-third of the beaten egg whites into the batter to lighten it. Fold in the remaining egg whites carefully, retaining as much air as possible.
07 - Pour the batter into the prepared cake pan and smooth the top evenly.
08 - Bake for 35–40 minutes until the top is golden and a toothpick inserted into the center comes out clean.
09 - Let the cake cool in the pan for 10 minutes. Run a knife around the edges, then invert onto a wire rack. Cool completely before serving.
10 - Dust with powdered sugar before serving if desired. Serve with fresh berries or whipped cream.