Crush crackers up fine. Melt butter. Mix the sugar, butter and crackers together and pat into a 9"x13" pan or dish. Save 1/4 cup to sprinkle on top of dessert when finished.
Mix 1 large package vanilla instant pudding mix with 1 1/2 cups milk. Mix the pudding until it is firm.
Soften 1/2 gallon vanilla ice cream. Fold the ice cream and pudding together and pour over the Ritz crackers.
Spread 1 (7 oz.) carton Cool Whip over the ice cream and pudding mixture. Sprinkle the remainder of the Ritz cracker crumbs on top of dessert. Freeze until ready to serve or sit out of freezer 1 hour then serve. Can make this dessert weeks ahead as long as it is covered well and frozen.