Coat the bottom and sides of a 9-inch spring form pan with the tablespoon of softened butter.  Break the chocolate wafers into the work bowl of a food processor and process to crumbs.  Add the melted butter, salt and cinnamon to the crumbs and process to combine.  Press the crumb mixture evenly over the bottom and up the sides to within 1 inch of the top of the pan.  Refrigerate crust 30 minutes.

Filling

1 1/2 pounds cream cheese, softened
1 cup sugar
3 Tablespoons unsweetened cocoa
Salt
4 eggs
1 pounds bittersweet chocolate, melted
3/4 cup sour cream
2 tablespoons butter, softened
1 teaspoon vanilla
* I add 1 teaspoon ground cinnamon and 1/4 teaspoon cayenne pepper, with 1 tablespoon very strong coffee made with a high concentrate of instant coffee and hot water.

Put cream cheese, 1/4 cup sugar, 2 tablespoons cocoa and 1/8  teaspoon salt in a large bowl; beat until smooth.  Beat remaining 3/4 cup sugar and eggs in another medium bowl until light, fluffy and tripled in volume, about 5 minutes. Beat egg mixture into cream cheese mixture, about 1/2 cup at a time.  Beat in melted chocolate.  Reduce the speed to low and beat in the sour cream and the butter and vanilla.

Adjust the oven rack to middle position and heat oven to 350ºF.  Pour filling into prepared crust, using a spatula to smooth the top surface of the filling.  Bake 10 minutes; reduce oven temperature to 325º and continue to bake until cake is set, about 35 minutes.  Transfer pan to a wire rack; cool completely, the refrigerate over night.  (Can refrigerate 3 days or freeze 1 month.)
Serving:  Run a knife around the edge of the cake to loosen it.  Carefully remove the pan rim.  Sprinkle the remaining cocoa over the top.  Cut into slices and serve.  Makes 24 servings.