Add room temperature egg whites to a standup mixer. Attach the whisk to the mixer and start beating the egg whites at the lowest speed. Slowly increase the speed to medium after a couple of minutes. Continue beating until it starts to look frothy. Then add in the cream of tartar.
Check to see if the egg whites start to form a soft peak. Then continue to beat it and slowly add in the (1/2 cup) sugar. Let it mix for another couple of minutes and check to see if it has formed a stiff peak. Add the egg whites to a large mixing bowl and set aside.
Whisk the dry ingredients in the standup mixer's bowl; cake flour, (3/4 cup) sugar, baking powder, and salt. Transfer it to the mixer and add in the oil, eggs, water, nectar concentrate, and vanilla extract.
Preheat the oven to 350°. Mix it on medium low speed for a minute then increase the speed for two more minutes until it is combined well enough.
Pour batter into the bowl with the whipped egg whites and gently fold everything together. Do not stir vigorously because it will deflate the the air bubbles in the egg whites. The air bubbles are needed to give the cake that fluffy texture.
Line parchment paper on a 9x13 inch baking pan. Pour the batter into the pan and bake it for 30-35 minutes.
Check to make sure the cake has thoroughly been baked by poking a toothpick into the middle of the cake. If it comes out clean, the cake is done. Set the cake on a hot pad and let it cool completely.