1. Preheat oven to 350ºF. Grease 10" springform pan. 2. In heavy 3-quart saucepan over low heat, heat semisweet chocolate, butter, sugar, half-and half or light cream, vanilla and salt, stirring frequently until chocolate melts and mixture is smooth.
3. In large bowl, with wire whisk or fork, beat eggs slightly; slowly beat warm chocolate mixture into eggs until well blended.
4. Pour batter into springform pan so that it spreads evenly.
5. Bake 45 minutes or until toothpick inserted in cake 2 inches from edge comes out clean. Cool cake completely in pan on wire rack.
6. When cake is cool, carefully remove side of pan; wrap cake, still on pan bottom, in plastic wrap and refrigerate until well chilled, at least 6 hours.
7. Prepare chocolate glaze.
8. Unwrap cake; remove from pan bottom. Line cake plate with waxed-paper strips. Place cake on plate and spread with warm glaze. (Spreading with metal spatula over top and sides.) Discard waxed paper.
9. Whip cream and spoon into pastry bag fitted with a medium star tube and pipe around to edge of cake . Refrigerate cake if not serving right away. Pull out a few minutes before serving.