Heat the oven to 325 degrees F. Put the egg whites in the bowl of a heavy-duty electric mixer. Set aside until the whites are slightly below room temperature, 60 degrees F, about 1 hour.

Sift the cake flour, confectioners' sugar, and salt onto a sheet of waxed paper; set aside.

Whip the whites on medium-low speed until frothy. Add the cream of tartar; turn the speed to medium. Continue whipping until soft peaks form. In a slow, continuous stream, add the granulated sugar, whipping until the whites thicken and form soft, droopy peaks. In the final moments of whipping, add the vanilla and lemon zest. The mixture should be fluffy but fluid enough to pour.

Sprinkle one-quarter of the flour mixture over the whites and, using a rubber spatula, gently fold the dry ingredients into the whites. Continue folding in the flour mixture, one-quarter at a time, until it has all been added.

Gently pour the batter into an ungreased 10-inch tube pan. Bake in the bottom third of the oven until the top is light golden and the cake feels spongy and springs back when touched, 45 to 50 minutes. Invert the pan onto the neck of a bottle or a funnel and let cool completely before removing from the pan.

To remove the cake from the pan, tilt the pan on its side and gently tap the bottom against the counter to loosen the cake. Rotate the pan, tapping a few more times as you turn it, until the cake comes free from the sides of the pan. Lift the cake from the pan. It should come out cleanly, leaving the crust on the sides of the pan. To serve, use a serrated knife and cut with a gentle sawing motion. Top with sugared berries, if you like.