Preheat oven to 350° F. Line two 8-inch cake rounds with parchment paper. Brush with oil. Set aside.
In the bowl of a stand mixer, combine egg whites and cream of tartar. Using a whisk attachment, mix on low speed until mixture is foamy. Increase speed to medium and slowly add ½ cup sugar, one tablespoon at a time.
Once all sugar has been added, increase speed and continue to mix until mixture is stiff peaks. Mixture should be shiny, smooth, and fluffy. Set aside.
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.
Add egg white mixture to cake batter in three additions. Gently fold to combine. The batter will slowly loosen as the egg whites are added.
Divide the batter evenly between the prepared pans. Bake for 18-20 minutes until tops of cake are 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 cake before unmolding. Let cake cool on wire racks.