Heat the oven to 325°F. Set a clean, completely dry 10-inch tube pan nearby, and do not grease it.

Sift the cake flour with about half of the granulated sugar two or three times. This distributes the flour evenly and helps create a fine, light crumb.

Beat the egg whites with the cream of tartar and salt until foamy. Add the remaining sugar gradually while beating until the whites are glossy and form medium-stiff peaks.

Beat in the vanilla just until combined. Stop before the whites become dry, grainy, or difficult to fold.

Fold the flour-and-sugar mixture into the beaten whites in several additions. Use a wide spatula and gentle strokes, stopping as soon as no dry streaks remain.

Spoon the batter into the ungreased tube pan and smooth the top. Run a knife or spatula gently through the batter to remove large air pockets.

Bake for 35–45 minutes, until the top is golden brown and springs back lightly when touched. Immediately invert the pan onto its feet or over a bottle and cool completely for 1–2 hours.

Run a thin knife around the edges if needed, then release the cake from the pan. Slice with a serrated knife and serve.