In large bowl, beat chocolate mixture, sugar, vanilla and eggs with electric mixer on medium speed 1 minute, scraping bowl occasionally. Beat in flour and salt on low speed 30 seconds, scraping bowl occasionally. Beat on medium speed 1 minute. Stir in nuts. Spread 1 3/4 cups of the batter in pan. Spread filling over batter. Drop remaining batter in mounds randomly over filling; carefully spread to cover cream cheese layer.