Cocoa Chiffon Cake

• 5 egg whites at room temperature
• 1 egg yolk
• 1 extra for dusting cake (plus)
• 250 gr sugar
• 190 gr sifted cake flour
• 120 ml vegetable oil
• 28 gr cocoa sifted
• 26 gr confectioners sugar sifted
• 9 gr baking powder
• 9 gr vanilla extract