Preheat oven to 350ยบ. Grease the bottom and sides of a 9x13 inch baking dish.
Beat all cream cheese filling ingredients in a bowl with an electric mixer on medium speed until smooth; set aside.
In a saucepan melt butter and chocolate over low heat, stirring frequently. Remove from heat and cool 5 minutes.
Beat chocolate mixture, sugar, vanilla, and eggs in a large bowl with an electric mixer on medium speed for 1 minute. Beat in flour and salt on low speed for 30 seconds. Beat on medium speed 1 minute.
Spread 1 3/4 cups of the batter in the pan. Spread filling over the batter. Drop remaining batter in mounds randomly over filling. Carefully run a knife in soft zig zags through to create a marbled look.
Bake 40-50 minutes or until cake tester inserted in the center comes out clean. Cool completely in the pan on a wire rack, about 2 hours. Cut into 8 rows by 6 rows.