Beat cream cheese and sour cream until smooth. Blend reserved cake mix, water, sugar and 2 eggs into cream cheese mixture on low speed, scraping bowl constantly, 30 seconds. Beat on medium speed, scraping bowl occasionally, 2 minutes. Reserve 1 1/4 cups cream cheese mixture; pour remaining mixture over crust. Blend reserved cream cheese mixture and Marbling Mixture in small bowl on low speed. Drop dark batter by generous tablespoonfuls randomly in 6 to 8 mounds onto yellow batter. Cut through batter with knife in S-shaped curves in one continuous motion. Turn pan 1/4 turn and repeat for marbled effect.

Bake until set and cake springs back when touched lightly in center, 31 to 36 minutes. Run knife along edges of cake to prevent cracking; cool completely. Refrigerate until firm. Cut into 2 1/4 x 1-inch bars. Top with fruit pie filling if desired. Refrigerate any remaining bars. 48 bars.

High Altitude Directions (3500 to 6500 feet) : Increase water to 2/3 cup and decrease sugar to 1/2 cup. (Cracking is normal.)