1. Heat oven to 325°F. Line 13x9-inch baking pan with foil, with ends extending over sides. Finely crush 24 cookies. Melt 1/4 cup butter; mix with crumbs. Press onto bottom of prepared pan.
2. Beat cream cheese and sugar with mixer until blended. Add sour cream and vanilla; mix well. Add eggs, 1 at a time, beating after each just until blended. Chop remaining cookies. Gently stir into batter; pour over crust.
3. Babke 45 min. or until center is almost set. Cool. Meanwhile, microwave chocolate and remaining butter in microwaveable bowl on HIGH 1 min.; stir until smooth. Cool slightly; spread over top of cheesecake. Refrigerate 4 hours. Use foil handles to lift cheesecake from pan before cutting to serve.
Cook's Note: How to make mess-free cookie crumbs: Crushing cookies into crumbs can be a messy task. To keep the mess to a minimum, place the whole cookies in a resealable plastic bag. Flatten bag to remove excess air, then seal bag. Crush the cookies into crumbs by rolling a rolling pin across the bag until the crumbs are as fine as you need. How to neatly cut dessert bars: When cutting creamy-textured desserts, such as cheesecake, carefully wipe off the knife blade between cuts with a clean damp towel. This prevents the creamy filling from building up on the blade, ensuring clean cuts that leave the edges intact.