Place egg whites in a large bowl; let stand at room temperature 30 minutes., Preheat oven to 325°. In a small bowl, mix flour and 3/4 cup sugar until blended., Add seeds from vanilla bean (or extract if using), cream of tartar and salt to egg whites. Beat on medium speed until soft peaks form. Gradually add remaining 3/4 cup sugar, 1 tablespoon at a time, beating on high after each addition until sugar is dissolved. Continue beating until soft glossy peaks form. Gradually fold in flour mixture, about 1/2 cup at a time., Gently transfer batter to an ungreased 10-in. tube pan. Cut through batter with a knife to remove air pockets. Bake on lowest oven rack until top springs back when lightly touched, 45-55 minutes. Immediately invert pan; cool completely in pan, about 1-1/2 hours. , Run a knife around sides and center tube of pan. Remove cake to a serving plate., For glaze, in a small bowl, mix confectioners' sugar, seeds from vanilla bean (or extract if using) and enough milk to reach desired consistency. Spread glaze over cake, allowing some to drip down sides.