In large mixing bowl at high speed, beat egg whites with cream of tartar until foamy. Add half of the sugar, 2 tablespoons at a time, beating constantly until sugar is dissolved and whites are glossy and stand in soft peaks. Rub just a bit of meringue between thumb and forefinger to feel if sugar has dissolved.
In small mixing bowl at high speed, beat egg yolks until thick and lemon-colored, about 3 to 5 minutes. Gradually beat in remaining sugar, liquid (if used), vanilla and salt (if desired) until blended.
Sprinkle flour over whites. Add beaten yolk mixture. Gently, but thoroughly, fold yolk mixture and flour into whites. Pour into ungreased 9x3-1/2 inch tube pan. Gently cut through batter with metal spatula or knife and spread evenly.
Bake in preheated 325° to 350°F oven until top springs back when lightly touched with finger and cake begins to pull away from sides of pan, about 35 to 45 minutes. Invert cake in pan on funnel or bottlene.