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. Stir gently just until combined, being careful not to overmix.
05 - In a clean bowl, beat the egg whites with an electric mixer until stiff peaks form. The whites should stand up firmly when the beaters are lifted.
06 - Gently fold one-third of the beaten egg whites into the batter to lighten the mixture. Fold in the remaining egg whites carefully, using a rubber spatula and retaining as much air as possible.
07 - Pour the batter into the prepared cake pan. Smooth the top with an offset spatula or the back of a spoon.
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 loosen, then invert onto a wire rack to cool completely.
10 - Dust generously with powdered sugar before serving. Serve plain or with fresh berries and whipped cream.