Preheat oven to 350 F (180C) and prepare your cake pan by lightly greasing and lining with parchment paper or flouring. I used a 9 inch springform pan, you can also use a bundt cake.
Using your fingertips, work the orange zest into the sugar until the sugar has moistened and turned fragrant and changed into a pale yellow/orange color.
In the bowl of a mixer fitted with paddle or whisk attachment, mix the egg yolks, orange zest scented sugar, vanilla, and orange blossom water on medium high speed for 2-3 minutes or until pale yellow and fluffy.
Add the oil and the butter and mix until well combined.
Add the flour and baking powder and mix until just combined, then add the juice and mix until combined.
In a separate bowl (either with a handheld mixer, or transfer the cake batter to another bowl and thoroughly wash and dry the mixer bowl) use an electric whisk to whisk the egg whites on medium high speed for 2-4 minutes until they form peaks that hold their shape.
Fold the egg whites into the cake batter with a rubber spatula, I like to do this in three additions. Take care not to deflate the egg whites.
Pour batter into prepared cake pan and bake for 50-60 minutes or until skewer inserted in the center comes out clean. If the outside of the cake is browning too rapidly and the inside still isn't cook, cover loosely with foil for the remainder of the baking time. Start checking at 40 minutes, every oven is different.
Cool before unmolding from the pan and serve plain, dusted with powdered sugar, or with whipped cream and berries. Delicious!