HEAT oven to 350 °F. Cover bottom of 9-inch springform pan with parchment paper. Combine chopped pecans, margarine and 2 Tbsp. sugar; press onto bottom of pan. Microwave caramels and milk in microwaveable bowl on MEDIUM 4 to 5 min. or until caramels are completely melted and mixture is well blended, stirring every 2 min. Spread over crust to within 1 inch of edge; cool.
BEAT cream cheese and remaining sugar with mixer until blended. Add eggs, 1 at a time, mixing on low speed after each just until blended. Stir in chocolate; pour over caramel layer.
BAKE 45 to 50 min. or until centre is almost set. Run knife or metal spatula around rim of pan to loosen cake; cool before removing rim. Refrigerate 4 hours. Sprinkle with pecans halves just before serving.