Pareve kosher-for-Passover margarine, melted
1¼ cups whole almonds (6 to 7 ounces)
1 cup sugar, divided
6 ounces bittersweet (not unsweetened) or semisweet chocolate, coarsely chopped
½ cup unsweetened cocoa powder
½ cup orange juice
2 teaspoons grated orange peel
6 large eggs, separated
1 vanilla bean, split lengthwise
¼ teaspoon salt
Preheat oven to 350°F. Brush bottom of 10-inch-diameter springform pan generously with margarine. Blend almonds and 1/4 cup sugar in processor until almonds are finely ground. Add chocolate; blend until chocolate is finely ground, scraping sides and bottom of bowl occasionally.
Whisk cocoa, orange juice, and orange peel in small bowl until smooth. Combine egg yolks and 1/2 cup plus 2 tablespoons sugar in large bowl. Scrape in seeds from vanilla bean. Using electric mixer, beat until yolk mixture is very thick, about 4 minutes. Beat in cocoa mixture. Fold in ground-almond mixture. Using clean dry beaters, beat egg whites and salt in another large bowl until soft peaks form. Gradually add 2 tablespoons sugar, beating until whites are stiff but not dry. Fold whites into chocolate batter in 3 additions. Transfer to prepared pan.
Bake cake until tester inserted into center comes out clean, about 40 minutes. Cool cake completely in pan on rack. (Can be made 1 day ahead. Cover with foil; store at room temperature.)
Cut around cake in pan; release sides. Cut cake into wedges. Transfer to plates. Place scoop of sorbet alongside.
Adapted from Epicurious.com