Prepare Oven and Ingredients: Position your oven rack in the lower-middle area and preheat the oven to 325°F (163°C). Gather all ingredients so they are ready to use, ensuring egg whites are at room temperature for optimal volume.
Create Fine Sugar-Flour Blend: Using a food processor or blender, pulse the granulated sugar until it reaches a powdery, superfine consistency. Reserve 1 cup of this processed sugar for whipping the egg whites. Into the remaining sugar, add the cake flour and salt, then pulse gently 5-10 times until the mixture is light and airy.
Whip Egg Whites to Soft Peaks: In a large mixing bowl, combine egg whites and cream of tartar. Using a hand or stand mixer with a whisk attachment, beat on medium-low speed until frothy, about one minute. Gradually add the reserved 1 cup of superfine sugar while increasing the speed to medium-high. Continue whipping until soft peaks form (when the whites hold shape but tips curl gently). Mix in the vanilla extract until just combined.
Gently Fold in Dry Ingredients: Sift the flour-sugar mixture over the whipped egg whites in three portions. Carefully fold each addition into the whites with a silicone spatula, using a gentle motion to preserve the airiness. Avoid overmixing to maintain a light batter.
Transfer Batter and Bake: Pour the batter into an ungreased 9 or 10-inch angel food tube pan. Smooth the surface by lightly tapping the pan on the countertop. Bake for 40-45 minutes, rotating the pan halfway through to ensure even baking. The cake should rise tall and turn golden.
Cool Cake Upside Down: Immediately invert the pan onto a cooling rack or use the pan’s feet if it has them. Allow the cake to cool completely for about 3 hours. This prevents the cake from collapsing and maintains its structure.
Remove and Serve: Once cool, run a thin knife around the edges of the pan to loosen the cake. Gently tap the pan on the counter until the cake releases. Dust with powdered sugar if desired, and slice carefully with a serrated knife. Serve plain or with whipped cream and fresh berries.