PREHEAT oven to 350°F. Combine sugar, cocoa and flour in medium saucepan. Add butter and milk. Bring to boil on medium heat, stirring constantly. Remove from heat. Stir small amount of hot mixture into eggs; return to hot mixture. Add half of the cherry pie filling; stir until well blended. Pour into crust.
BAKE 35 to 45 min. or until center is almost set. Cool. Refrigerate 1 hour.
ADD grated chocolate to 2 cups of the whipped topping; stir gently until well blended. Spread over pie; top with remaining cherry pie filling and the remaining whipped topping. Refrigerate at least 30 min. before serving. Store leftover pie in refrigerator.