Beat whites with a pinch of salt in another bowl with an electric mixer at medium speed until they hold soft peaks. Add remaining 2 tablespoons sugar a little at a time, beating, and beat until whites just hold stiff peaks. Fold one fourth of whites into chocolate mixture to lighten, then fold in remaining whites gently but thoroughly. Pour batter into springform pan, then bake until a wooden pick or skewer inserted in center comes out with a few moist crumbs adhering, 35 to 40 minutes. Transfer to a rack and cool completely in pan, about 1 hour. Run a knife around edge of torte to loosen, then remove side of pan. Dust with
Passover confectioners sugar.