Drain pineapple tidbits, reserving 1 cup juice; set aside. Combine instant pudding mix, 1/2 cup reserved juice and milk in a large bowl. Beat at low speed with an electric mixer 2 minutes until thickened. Fold in sour cream and pineapple tidbits. Place 1/3 of cake cubes in bottom of a 16-cup glass bowl; drizzle with 2 to 3 tablespoons remaining reserved pineapple juice. Spoon 1/3 of pudding mixture over cake. Repeat procedure twice, ending with pudding mixture. Cover and chill at least 3 hours. Just before serving, spread top with whipped topping. Garnish, if desired. Yield: 12 servings.