Prepare the Oven and Pan: Preheat the oven to 350°F. Place the oven rack in the middle position. Use an untreated aluminum tube pan (10-inch diameter, 4-inch depth) with a removable bottom. Ensure it is clean and dry; nonstick pans are not suitable.
Sift the Flour: Measure the bleached cake flour and sift it. If using a measuring cup, spoon flour into the cup and level it with a knife before sifting.
Make the Meringue: In a stand mixer fitted with a whisk attachment, combine the egg whites, sugar, and vanilla. Mix on low for 1 minute until moistened, then increase to medium-low speed and whip for 3 minutes. The mixture will become dense and slightly dark from the vanilla.
Add Stability: Add lemon juice and salt. Increase the speed to medium and whip for 3 minutes. The meringue will become lighter but not foamy. Increase to medium-high speed and continue whipping until it forms very soft peaks (whisk detachment test: it should softly collapse).
Incorporate the Flour: Gently sprinkle the sifted cake flour over the meringue. Using a spatula, fold the flour in gently, starting from the bottom and working upward. Avoid overmixing. Pour the batter into the tube pan until it’s two-thirds full.
Bake the Cake: Bake for 45 minutes or until the cake rises well above the rim of the pan and develops a firm, golden-brown crust. The internal temperature should reach 206°F.
Cool the Cake: Immediately invert the pan on its stilts or rest it over a bottle. Allow it to cool completely, at least 2 hours, to set its structure.
Unmold and Serve: Once cooled, loosen the cake by sliding a metal spatula around the edges, including the center tube. Turn the cake out onto a serving plate. Slice with a serrated knife into 10-12 servings and enjoy.