Heat oven to 325 degrees F. Mix cookie crumbs and margarine; press onto bottom of foil-lined 13x9-inch pan. Bake 10 min.

Beat cream cheese, sugar and vanilla in large bowl with mixer until blended. Add sour cream; mix well. Add eggs, 1 at a time, mixing after each just until blended.

Reserve 1 cup batter. Stir chocolate into remaining batter; pour over crust. Top with spoonfuls of reserved batter.

Swirl batters with knife. Bake 40 min. or until centre is almost set. Cool. Refrigerate 4 hours.