HEAT oven to 350ºF. PREPARE cake batter and bake in 2 (9-inch) round pans as directed on package. Cool cakes in pans 10 min. Invert onto wire racks; gently remove pans. Cool cakes completely. Microwave chocolate and butter in small microwaveable bowl on HIGH 2 mins. or until butter is melted. Stir until chocolate is completely melted.
Cool 5 min. Meanwhile, beat cream cheese and sugar in large bowl with mixer until blended. Gently stir in cool whip and crushed cookies. PLACE 1 cake layer on plate, spread with cream cheese mixture. Top with remaining cake layer. Spread top with chocolate glaze; let stand 10 mins. or until firm. Keep refrigerated.