Heat oven to 350°F. Grease bottom and sides of 13x9-inch pan with shortening.
In medium bowl, beat all filling ingredients with electric mixer on medium speed until smooth; set aside.
In 1-quart saucepan, melt butter and chocolate over low heat, stirring frequently. Remove from heat; cool 5 minutes.
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.
Bake 45 to 50 minutes or until toothpick inserted in center comes out clean. Cool completely in pan on wire rack, about 2 hours. For brownies, cut into 8 rows by 6 rows. Store covered in refrigerator.