HEAT oven to 350°F.
MIX cookie crumbs and butter until blended; press onto bottom and 1 inch up side of 9-inch springform pan. Microwave 6 oz. chocolate and half-and-half in medium microwaveable bowl on HIGH 1 to 1-1/2 min. or until chocolate is completely melted and mixture is well blended when stirred. Add sugar; mix well. Blend in eggs. Stir in nuts. Pour into crust; place on baking sheet.
BAKE 35 to 40 min. or until center is almost set. Cool 15 min. Run knife around rim of pan to loosen dessert; cool before removing rim.
MICROWAVE remaining chocolate and peanut butter in microwaveable bowl on HIGH 45 to 55 sec. or until chocolate is completely melted and mixture is well blended when stirred. Spread over tart. Refrigerate 3 hours.