The freezer tray of your automatic refrigerator makes wonderful cake-and-ice-cream specialties in jig time. FROZEN LADYFINGERS: Pack tray two thirds full with vanilla ice cream. Split ladyfingers, sprinkle generously with rum- arrange crosswise, with flat sides down, on ice cream. Freeze. Before serving, spread generous layer whipped cream over ladyfingers. Serve sliced. BUTTERSCOTCH-ALMOND ICE-CREAM CAKE: Line bottom of tray with strips of bakers poundcake. Spread with 1 pt. vanilla, coffee, or chocolate ice cream. Freeze. Serve sliced, with butterscotch sauce and toasted almonds. CHOCOLATE CHARLOTTE: Slice 8 spongecake layer crosswise into 1/4"-thick slices. Use to line bottom and sides of tray. Sprinkle with 2 tablesp. sherry; then spread with 1/2 pt. chocolate ice cream. Top with rest of cake, with whipped cream. Makes 6 servings. FREEZER-TRAY TRIFLE: In tray, alternate layers of spongecake strips with layers of vanilla, coffee, chocolate, butter-pecan, or strawberry ice cream, ending with cake. Sprinkle with 1/4 cup rum. Freeze. Serve sliced with crushed berries and bottled eggnog sauce or custard sauce flavored with rum.