HEAT over to 350 degress. PREPARE cake batter and bake as directed on package for 2 (9-inch) round cake layers, blending dry pudding mix into batter before pouring into prepared pans. Cool 10 min. Loosen cakes from sides of pans with knife. Invert onto wire racks; gently remove pans. Cool cakes completely.
MEANWHILE, beat cream cheese, butter and vanilla in large bowl with mixer until blended. Gradually beat in sugar.
CUT each cake layer horizontally in half. Stack on plate, spreading 3/4 cup cream cheese frosting between each layer. Spread remaining frosting onto top and side of cake.
MICROWAVE COOL WHIP and chocolate in microwaveable bowl on HIGH 1-1/2 min., stirring after 1 min.; stir until chocolate is completely melted and mixture is well blended. Cool 5 min. Pour over cake, letting excess drip down side. Store cake in refrigerator.