PreparationFor crust: Position rack in center of oven and preheat to 325°F. Lightly butter 9-inch springform pan. Finely grind cookies, nuts and sugar in processor. Add butter and process until well blended. Press crumb mixture into bottom and 1 inch up sides of pan. For filling: Melt chocolate chips in heavy small saucepan over very low heat, stirring constantly. Remove from heat. Using electric mixer, beat cream cheese in large bowl until light and fluffy. Gradually beat in sugar. Add eggs 1 at a time, beating well after each addition. Add sour cream and remaining 3 ingredients and beat until just blended. Pour half of batter into medium bowl. Add melted chocolate to batter in medium bowl and mix well. Pour all but 2 tablespoons chocolate batter into prepared crust. Cover with plain batter. Using tip of knife, swirl batters together. Drizzle remaining 2 tablespoons chocolate batter over. Bake until tester inserted in center comes out clean, about 1 hour (cake may crack). Cool completely on rack. Cover with plastic and refrigerate overnight. (Can be prepared 2 days ahead.) For topping: Using electric mixer, beat cream cheese, sugar, sour cream, Frangelico and vanilla in medium bowl until smooth. Transfer to pastry bag fitted with medium star tip. Pipe decorative border around edge of cake. (Can be prepared 8 hours ahead. Chill.)
PreparationFor crust: Position rack in center of oven and preheat to 325°F. Lightly butter 9-inch springform pan. Finely grind cookies, nuts and sugar in processor. Add butter and process until well blended. Press crumb mixture into bottom and 1 inch up sides of pan. For filling: Melt chocolate chips in heavy small saucepan over very low heat, stirring constantly. Remove from heat. Using electric mixer, beat cream cheese in large bowl until light and fluffy. Gradually beat in sugar. Add eggs 1 at a time, beating well after each addition. Add sour cream and remaining 3 ingredients and beat until just blended. Pour half of batter into medium bowl. Add melted chocolate to batter in medium bowl and mix well. Pour all but 2 tablespoons chocolate batter into prepared crust. Cover with plain batter. Using tip of knife, swirl batters together. Drizzle remaining 2 tablespoons chocolate batter over. Bake until tester inserted in center comes out clean, about 1 hour (cake may crack). Cool completely on rack. Cover with plastic and refrigerate overnight. (Can be prepared 2 days ahead.) For topping: Using electric mixer, beat cream cheese, sugar, sour cream, Frangelico and vanilla in medium bowl until smooth. Transfer to pastry bag fitted with medium star tip. Pipe decorative border around edge of cake. (Can be prepared 8 hours ahead. Chill.)