Sift the flour, 3/4 cup of the sugar, salt and lemon zest together 3 times.
Beat the egg whites, water, lemon juice, cream of tartar and extracts together with an electric mixer on low speed until frothy. Increase to medium speed and beat until the mixture is 4 times its original volume, about 2 to 3 more minutes.
Continue beating and add the remaining sugar, gradually over 3 minutes.
Sift the flour mixture into the egg white mixture, 1/4 cup at a time with a spatula, working the batter as little as possible.
Pour the batter into an ungreased 10" tube pan. Run a knife around the center of the batter and tap the pan on the counter to remove any air pockets in the batter. Bake 45 to 50 minutes, until the cake is light golden brown and well risen.
Immediately invert the pan on the neck of a bottle until the cake is completely cool. Slide a knife around the pan and remove the cake. (This can be done in advance and stored in an airtight container for 1-2 days.).
For the icing:.
In a bowl, combine the egg whites, sugar, water, lemon juice, corn syrup and cream of tartar. Place the bowl over a pan of simmering water, stirring constantly with a rubber spatula until the sugar dissolves and the mixture is warm to the touch.
Remove from heat and beat with an electric mixer on medium-high speed until medium peaks form and the meringue is cool. Add the vanilla extract and lemon zest and mix on high speed until stiffer peaks form.
Place the cake on a serving platter and spread the icing over the top and sides of the cake. (Do not ice the cake more than 5 hours ahead or the frosting will lose volume and become grainy.).