Blend cake mix, water, oil, eggs and 1 cup sour cream in large bowl. Beat at low speed until moistened, then beat at medium speed for 2 minutes.
Pour into pans and bake according to package directions.
To assemble, place 1 cake layer on serving platter. Spread 3/4 cup cream cheese frosting on top of layer. Spread jam on top of cream cheese frosting. Top with remaining layer of cake. Frost top and sides of cake with chocolate frosting.
To prepare sauce, blend remaining cream cheese frosting and 1 cup sour cream in small bowl until smooth and creamy. Garnish top of frosted cake with 2-3 tbsp of sauce in center and fresh rasperries. Place 2 tablespoons sauce on center of each serving plate and top with slice of cake. Garnish with fresh raspberries, if desired.