Crust:
¼ cup butter, melted
1-1/2 cups chocolate cookie crumbs

Filling:
1-1/2 cups semisweet chocolate chips
2 tablespoons butter
¼ cup coffee liqueur
2 (8-ounce) packages cream cheese
2 eggs
1/3 cup sugar
1 cup sour cream

Topping:
¼ cup semisweet chocolate chips
1 tablespoon coffee liqueur
1 tablespoon corn syrup
1 cup sour cream

Preheat oven to 350 degrees.

Mix together crust ingredients and press into bottom of 9-inch springform pan; set aside.

To prepare filling: In a small saucepan, melted the chocolate, butter and liqueur over a low heat, stirring until smooth. Remove from heat and cool slightly.

In a large bowl, beat the cream cheese until fluffy. Add eggs, one at a time, beating well after each addition. Beat in sugar and sour cream. Slowly beat in chocolate mixture and pour filling into prepared crust. Bake for 1 hour. Turn off oven and leave cheese cake in oven 1 more hour. Remove from oven and cool in pan on a wire rack. Refrigerate until chilled, about 4 hours.

To prepare topping: In a small saucepan, melt the chocolate, liqueur and corn syrup, stilling until smooth. Cool to room temperature and drizzle over cake.