Sift the flour, 1 cup sugar, baking powder, and salt into a bowl.
2 cups (235g) cake flour, 1 cup (200g) granulated sugar, 1 Tbsp baking powder, 1 tsp salt
Make a well and add the egg yolks, vegetable oil, water, and vanilla. Set aside.
7 large egg yolks, 1/2 cup (120ml) vegetable oil, 3/4 cup (180ml) cold water, 1 Tbsp vanilla extract
In another large bowl, beat the egg whites until foamy. Add in the cream of tartar. Continue mixing and slowly add in the sugar. Beat until stiff peaks form. Set aside.
7 large egg whites, 1/2 tsp cream of tartar, 1/2 cup (100g) granulated sugar
Using the same beaters, beat the egg yolk batter. Scrape the bowl as needed. Beat until combined and smooth.
Fold in 1/4 of the egg whites into the egg yolk batter to lighten it up. Then gently fold in the rest of the egg whites in two equal parts until no white streaks remain.
Pour into an ungreased 10" tube pan with removable bottom. Bake for 55-60 minutes or until a toothpick inserted into the center comes out clean. The top should be golden brown and spring back when lightly pressed.
Let cool completely upside down. Unmold and serve. Slice using a serrated knife.
Notes
Leftovers can be stored in an airtight container or tightly wrap in saran wrap and left at room temperature for 3-4 days.You can also freeze chiffon cake once it's completely cooled. Tightly wrap it in a layer of saran wrap and a layer of aluminum foil. Store in the freezer for up to 3 months. Thaw in the refrigerator overnight.See above in post for expert tips and substitutions.