Position an oven rack in the bottom third of your oven and preheat the oven to 350°F. Have a 9 or 10-inch ungreased tube pan (16-cup capacity) ready.
Place the sugar in a food processor and blend until the sugar is very finely ground, about 1 minute. (This creates superfine sugar, perfect for dissolving into egg whites!) Remove 1 cup of the fine sugar (200g), leaving the rest in the food processor.
To the food processor, add the cake flour and salt. Pulse 10 times.
Set a fine mesh sieve over a medium bowl. Sift the reserved 1 cup of fine sugar into the bowl. Discard any large grains caught by the sieve.
Place the same sieve over a separate large bowl and add the sugar and flour mixture. Sift the sugar and flour together into the large bowl and set aside.
In a clean, large mixing bowl, combine the egg whites and cream of tartar. Use an electric hand mixer or a stand mixer fitted with the whisk attachment and beat the egg whites on low speed until they turn frothy on top, about 1 minute.
Once the egg whites become frothy, increase the speed to medium and sprinkle the reserved 1 cup of fine sugar 1 tablespoon at a time into the egg whites. Once the sugar is incorporated, beat the egg whites until soft, glossy peaks form. This will take about 5 minutes overall. Add the vanilla and beat on low speed just until incorporated.
Sift a third of the flour and sugar mixture over the egg whites and gently fold in the dry ingredients with a spatula. Repeat two more times.
Transfer the batter to a clean, ungreased tube pan. Smooth the top and clean off the sides of the pan. Gently tap the pan on the counter a few times or run a knife or skewer through the batter to help break up any large air bubbles that may have gotten trapped.
Bake for 35 to 40 minutes or until the cake is golden brown and a skewer inserted in the center comes out clean.
Invert the pan onto the counter and allow the cake to cool upside-down in the pan for at least 1 hour. Most angel food cake pans have feet at the top so the cake can cool upside down but if yours doesn't just invert onto a wire rack.
Once the cake is completely cooled, run a thin knife along the outer edge between the cake and the pan, and around the center tube, then pull the center-piece out to remove the cake. Run the knife along the bottom of the pan and invert onto a cake stand. Place the cake on a serving plate and dust with powdered sugar, if desired. Serve alone or with whipped cream and berries.
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Notes
Measure your flour correctly. Adding too much cake flour to the recipe is a common mistake that will throw off the texture of the angel food cake. The most accurate way to measure flour is by using a scale. If you don’t have one, fluff your flour with a spoon, sprinkle it into your measuring cup, and use a knife to level it off.
Keep the egg yolks out! Even a small amount of egg yolk can cause the egg whites to not whip up properly. Separate the eggs while cold to make it easier, and crack each one into an individual bowl before adding the whites to your measuring container. This way, if a yolk breaks, you don’t contaminate all of the egg whites.
Bring egg whites to room temperature. After separating the eggs, allow the egg whites to warm to room temperature. They will be much easier to aerate.
DO NOT grease/butter/oil your cake pan! The batter needs to cling to the wall of the pan to rise properly. It also needs to stick to the sides of the tube pan so it doesn’t fall out when you invert the pan to cool the cake.
Take care when folding in the dry ingredients. Incorporate them gently and be careful not to deflate the meringue.
Use a serrated knife to slice the cake. You cannot press down on a fluffy angel food cake without smashing it, so gently saw each slice with a sharp serrated knife, like a bread knife.