Preheat oven to 350°F and lightly grease a two piece tube pan with butter and dust lightly with flour. Shake out excess flour.
Separate the eggs placing the egg yolks in a large mixing bowl and the whites in the bowl of your stand mixer fitted with a whisk attachment.
Add the sugar and oil to the egg yolks and whisk vigorously for several minutes until the mixture is pale yellow, thick and forms ribbons when you lift the whisk out of the bowl.
Stir in the lemon rind and lemon juice. Add the sifted flour and baking powder. Stir until well combined.
Whisk the egg whites in the mixer on medium-high speed until the whites form stiff peaks, about 3-4 minutes.
Using a rubber spatula, gently fold half of the egg whites into the batter. When completely incorporated, fold in the remaining egg whites.
Pour the batter into the prepared cake pan and bake for 50 minutes in the center of the oven until a toothpick inserted in the cake comes out clean. Time may vary according to your oven.
When you remove the cake from the oven, gently turn it upside down on a flat surface and allow to cool completely before unmolding the cake, about an hour. Dust lightly with powdered sugar before serving.
A two piece tube cake pan or angel food cake pan with extended prongs is necessary to make this cake. When the pan is inverted it will stand on its prongs thus allowing air to circulate underneath to cool it.
Do not over flour the cake pan otherwise the cake may slip out when turned upside down. If the cake partially dislodges itself from the pan, leave it be and let it cool completely.
For best results, the eggs should be at room temperature.
Do not over stir the mixture once you've added the egg whites. Stir just until the egg whites are incorporated as the batter must remain light and airy.