Preheat the oven to 350ºF. Butter the sides and bottom of a 9-inch pan with 1 teaspoon of the butter.
In a food processor grind the chocolate wafers into fine crumbs. Add the remaining 5 tablespoons melted butter and 2 tablespoons of the granulated sugar and blend thoroughly. Press evenly into the bottom and partway up the sides of the springform pan.
In a bowl beat the cream cheese with an electric mixer at high speed until smooth and creamy, for about 5 minutes. Beat in the melted chocolate and the remaining 1/2 cup granulated sugar until thoroughly blended. Beat in the raspberry liqueur and continue beating until the mixture is very smooth, for about 4 minutes.
Set the mixer at low speed and add the eggs one at a time, beating each until incorporated but taking care not to overbeat. Add the heavy cream and beat just until incorporated, for about 30 seconds.
Pour the mixture into the crust in the springform pan and bake until firm, for about 50 minutes. The filling should seem soft in the middle; don’t overbake. Remove from the oven and allow to cool to room temperature.
In a small bowl whisk the sour cream together with the confectioners’ sugar until smooth and creamy. Spread this topping over the cooled cake and then refrigerate for at least 4 hours. Remove from the refrigerator and remove the springform ring.
To serve, top the cake with the raspberries and cut it into wedges.
Yield: one 9-inch cheesecake