Place chocolate in a double boiler and heat over hot water until it melts. Stir to blend and let cool to room temperature.
Microwave almonds and butter for crust for 1 minute. Stir dry crust ingredients together in 23 cm springform pan. Add butter and nuts and pat firmly onto bottom. Grease sides of pan.
With an electric mixer, blend cheese and sugar until smooth. Mix in eggs, vanilla, and sour cream. Stir in melted chocolate. NOTE: it is important to have the cheesecake ingredients and the melted chocolate close to the same temperature when they are combined so that they blend together smoothly. Pour into pan. Put another pan with water into the preheated oven. This will prevent the top of the cheesecake from cracking. Bake in the middle of a preheated 160ºC oven for 45 minutes or until just barely set. Turn off the oven, leave the door ajar, and let cool in oven for 1 hour longer. Chill. Just before serving, dust cocoa through a sieve making a ring around the cheesecake.
Prepare raspberry sauce: Reserve half cup raspberries for garnish. In a blender, puree the remaining berries and push through a sieve. Stir in sugar to taste and the Grand Marnier. To serve, spoon raspberry sauce on to desert plates. Remove pan sides of cheesecake and cut into wedges. Place on raspberry sauce and garnish with berries.