Mix sugar, flour, 1/4 cup milk and eggs until blended; stir in melted chocolate.
Pour into 9-inch square pan sprayed with cooking spray.
Bake 25 min. or until toothpick inserted in center comes out clean. (Do not overbake.) Cool completely.
Beat pudding mix and remaining milk in medium bowl with whisk 2 min. Stir in COOL WHIP; spread over dessert. Melt remaining chocolate; drizzle over pudding layer. Refrigerate until chocolate is firm.