Preheat oven to 350° F. Line two 8-inch cake rounds with parchment paper and brush lightly with oil. Set aside.
Meringue: In a stand mixer bowl, combine egg whites and cream of tartar. Using a whisk attachment, mix on low speed until mixture is foamy. Increase speed to medium and gradually add ½ cup sugar, one tablespoon at a time. Once all the sugar is incorporated, increase speed and whip to stiff, glossy peaks. Set aside.
Base Batter: In a medium bowl, whisk together cake flour, baking powder and remaining ½ cup of granulated sugar. In a larger bowl, whisk together vegetable oil, water, vanilla, egg yolks, and salt. Add dry mixture in three additions to wet mixture. Fold to combine. Mixture should be smooth, shiny, and thick.
Fold Together: Add meringue to base batter in three additions, folding gently but thoroughly. The batter will gradually loosen as you incorporate the whites.
Bake: Divide cake batter evenly between prepared pans. Bake for 18-20 minutes until lightly golden brown and a toothpick inserted in center of cake comes out clean. Let cool in pan for 5-10 minutes. Run mini offset spatula around the edges of the cake pan to loosen. Turn out onto wire racks to cool further.