For Glaze: Combine cream, butter and sugar in heavy large saucepan. Stir over medium heat until butter melts, sugar dissolves and mixture comes to simmer. Remove from heat. Add chocolate and vanilla. Stir until chocolate melts and glaze is smooth. Let stand until thick enough to spread, stirring occasionally, about 1 hour. (Can be made 1 week ahead. Cover and refrigerate. Before using, whisk over low heat just until spreadable.)
For cake: Preheat oven to 350°F.
Butter two 9-inch-diameter cake pans with 2-inch-high sides. Line pan bottoms with waxed paper; butter paper. Stir chocolate in top of double boiler set over simmering water until melted. Remove from over water.
Sift flour, cocoa, baking soda and salt into medium bowl. Using electric mixer, beat sugar and butter in large bowl until well blended. Add eggs 1 at a time, beating to blend after each addition and occasionally scraping down sides of bowl. Mix in melted chocolate and vanilla. Mix in dry ingredients alternately with buttermilk in 3 additions each. Transfer batter to prepared pans, dividing equally.
Bake cakes until tester inserted into center comes out clean, about 35 minutes. Cool cakes in pans on racks 10 minutes. Cut around pan sides to loosen cakes. Turn cakes out onto racks; peel off waxed paper. Cool cakes completely. (Can be prepared 1 day ahead. Wrap tightly and store at room temperature.)
For filling: Using electric mixer, beat cream, powdered sugar, framboise (if desired) and vanilla in large bowl until very firm peaks form. Transfer 1 1/2 cups whipped cream mixture to small bowl and chill. Fold 2 cups raspberries into remaining whipped cream mixture.
Cut each cake layer horizontally in half. Using large tart pan bottom as aid, transfer 1 layer to platter. Slide waxed paper strips under edges of cake. Spread 2/3 cup chocolate glaze over cake. Spread half of raspberry whipped cream over. Place second cake layer on work surface. Spread 2/3 cup glaze, then remaining raspberry cream over. Place atop first layer, using tart pan as aid. Top with third cake layer, pressing lightly to adhere (reserve fourth layer for another use). Smooth filling at edges of cake. Spread thin layer of glaze over sides of cake. Chill until glaze sets, about 10 minutes.
Spread remaining glaze over sides of cake. Spread or pipe reserved 1 1/2 cups whipped cream mixture over top of cake. Garnish with additional berries, if desired. Gently remove waxed paper from under cake. Cover cake with cake dome; chill at least 1 hour and up to 8 hours.