CHOCOLATE CRUMB CRUST:
11/3 cups Oreo cookie crumbs
1 tablespoon sugar
4 tablespoons (1/2 stick) butter, at room temperature
Mix cookie crumbs with sugar and butter. Pat in an even layer over bottom of a 9-inch springform pan.
1/4 cup Kahlúa
11/2 cups semisweet chocolate chips
2 tablespoons butter
1/3 cup sugar
1/4 teaspoon salt
1 cup (1/2 pint) sour cream
2 (8-ounce) packages cream cheese, room temperature
1/2 cup sour cream, for topping
Put Kahlúa, chocolate chips, and butter in small saucepan over low heat. Stir constantly until chocolate melts and mixture is smooth; set aside to cool slightly. Heat oven to 325°. Beat eggs in small bowl. Beat in sugar, salt, and sour cream. Drop small pieces of cream cheese into egg mixture, continuing to beat until smooth. Gradually beat in chocolate mixture. Pour into springform pan over crust. Bake until filling is just barely set in center, about 40 minutes.
Take pan out of oven and let stand at room temperature 1 hour. Spread on 1/2 cup sour cream; refrigerate cheesecake several hours.
Kahlúa Chocolate Sauce:
1 cup semisweet chocolate chips
1/3 cup Kahlúa
1/3 cup light corn syrup
Heat chocolate chips with Kahlúa and corn syrup over low heat until chocolate melts and mixture is smooth.
Unhinge pan and cut cold cheesecake in small slices with thin, sharp knife dipped in cold water. Dip knife before each cut, and wipe clean between cuts. Pour a bit of sauce over top of each slice. Yields 12 servings.