Preheat your oven to 375ºF. It's important that the oven is fully pre-heated before you put the cake in the oven, which can take up to 30 minutes.
To ensure your bowl and whisk are clean, wipe them out with a clean towel and some white vinegar to remove any bits of fat that might be there.
Sift together the first quantity of sugar, flour, and cornstarch into a large bowl and set it aside.
Weigh the egg whites into the bowl of a stand mixer with a food scale. Whip with the whisk attachment on medium for 30 seconds until they start to get foamy.
Reduce the speed to low and add in your cream of tartar, salt, and vanilla.
Continue mixing on low and begin sprinkling in the second amount of remaining sugar.
Increase to medium speed and whip the mixture to soft but firm peaks. They should look glossy and moist and the peaks should gently fold over when you scoop them.
Sift the dry ingredients into the egg mixture about ⅓ cup at a time and gently fold them together with a rubber spatula. Refer to the video to see how to fold properly. The idea is to avoid knocking any air out of the meringue while folding to keep the batter very fluffy.
Repeat this sifting and folding process until all of the flour mixture has been folded into the meringue.
Carefully pour the angel food cake batter into an ungreased tube pan. You need the cake to stick to the sides of the pan to help it rise while it's baking.
Slide a knife or offset spatula through the batter to pull out any big air bubbles that might be trapped in there. Smooth the top with a spoon so the batter is level.
Bake the angel food cake in the oven on the center rack for 40-45 minutes or until the top is lightly golden brown and the top springs back when you touch it.
Take the cake out of the oven and cool it upside down for about 1 hour. Some tube pans have little feet that hold the pan upside down or the center tube might just be a little taller than the sides. If your pan doesn't have these options you can cool the pan upside down on a wine bottle to keep it elevated. Cooling the cake upside down helps the cake keep its volume.
Once the pan is completely cool, you can slide a butter knife between the cake and the pan to detach the cake. If it's an invert pan with a removable bottom, you can push it out now or just give the cake a couple of gentle shakes to get the cake to come out.
I like to dust the top of the cake with some powdered sugar and add some whipped cream and fresh strawberries but the possibilities are endless! This is easiest to slice with a serrated knife.
Store the cake at room temperature for up to 4 days (without whipped cream) in an airtight container or covered it with plastic wrap.