01 - Preheat the oven to 325°F. Line the bottom of an 8-inch round cake pan with parchment paper. Do not grease the sides.
02 - In a medium bowl, whisk together the flour, sugar, baking powder, and salt until well blended.
03 - In a large bowl, whisk together the egg yolks, Greek yogurt, vegetable oil, vanilla extract, and lemon zest 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. Then carefully fold in the remaining egg whites, retaining as much air as possible.
07 - Pour the batter into the prepared cake pan and smooth the top with a spatula.
08 - Bake for 35–40 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. Cool completely.
10 - Dust with powdered sugar before serving, if desired. Serve with fresh berries or whipped cream.