Vanilla Chiffon Cake with Chocolate Sorbet

Preheat oven to 350°F. Blend 1/2 cup sugar, matzo cake meal, potato starch, vanilla beans and salt in processor until beans are finely chopped. Sift mixture into small bowl; discard beans in sieve.

Using electric mixer, beat egg whites in large bowl until medium-firm peaks form. Gradually add 3/4 cup sugar, beating until stiff but not dry. Using the same beaters, beat yolks and 1/4 cup sugar in another bowl until thick, about 5 minutes. Gradually beat in oil, then brandy. Beat in matzo mixture. Fold in whites in 3 additions.

Transfer batter to ungreased 10-inch-diameter tube pan with removable bottom. Bake until tester inserted near center comes out clean, about 37 minutes. Immediately invert center tube pan onto narrow-neck bottle. Cool completely. (Can be made 1 day ahead. Cover cake in pan.)

Cut around pan sides to loosed cake. Cut into wedges; serve with sorbet.