Place the oven rack in the middle position, and preheat oven to 350°F.
Set a 10-inch aluminum tube (angel food cake) pan nearby. Do not grease or butter the pan.
Shake flour through a fine-mesh sieve or sift it and set aside.
18 tablespoons bleached cake flour
In the bowl of a stand mixer fitted with the whisk attachment, combine the egg whites, sugar, and vanilla extract. Mix on low for 1 minute, then increase speed to medium-low and whip for 3 minutes. The whites will look darker and will still be thick.
2 cups egg whites, 2 cups granulated sugar, 1 tablespoon pure vanilla extract
With the mixer running, add the lemon juice and salt.
2 tablespoons freshly squeezed lemon juice, ¼ teaspoon kosher salt
Set the speed to medium and whisk the meringue for 3 more minutes. At this stage, the meringue will be foamy and thin.
Increase the speed to medium-high and whip for another 2-4 minutes. The meringue should be glossy white and thick(ish), but not to the stiff-peak stage. It should still be soft enough to run off the wires of the whisk, when lifted, and mound like soft-serve ice cream in the bowl.
Sprinkle cake flour over the meringue and use a clean and dry rubber spatula to fold the flour into the meringue. Fold the flour by scraping from the bottom up and folding through the center. Fold the flour until no pockets of flour remain.
Spoon the batter into the (ungreased) tube pan and gently smooth it out on top. Give the pan a couple of gentle raps on the counter to release any large air bubbles.
Bake at 350°F 40-50 minutes, or until the cake has risen and is golden blond and somewhat firm to the touch. The internal temperature should read 206°F on a food thermometer.
Angel Food Cake has to be placed upside down to cool completely for at least 2 hours. If your pan has stilts, invert it onto its stilts over a clean kitchen towel. If your pan doesn’t have stilts, invert it onto a trio of cans.
Slide a thin knife or an offset spatula around the sides and around the center tube to loosen the cake. Lift the cake by the center tube and set it on the counter. Loosen the bottom of the cake by sliding a knife between the cake and the bottom of the pan’s insert. Place one hand on each side of the cake and carefully lift the cake off the center tube. Set the cake on a cake tray or serving plate.