Step 1

Line a 9-inch square baking pan with foil, extending foil over edges. For crust, in a small bowl stir together cookie crumbs, granulated sugar, and nuts. Stir in melted butter until combined. Press into prepared pan.

Step 2

For filling, in a large bowl combine next four ingredients (through liqueur). Beat with a mixer on medium until smooth. Gradually beat in powdered sugar. Beat on medium to high 2 to 3 minutes or until light and fluffy. Carefully spread filling over crust. Cover and chill 1 hour or until firm.

Step 3

For topping, in a small saucepan cook and stir bittersweet chocolate and 1/4 cup butter over low heat until melted. Spread over filling. If desired, drizzle or spoon melted white chocolate over topping; swirl slightly with a toothpick to marble. Cover and chill 2 hours or until firm. Using foil, lift out uncut cookies. Cut into bars.