Heat oven to 350* Generously grease bottom only of a 13x9" pan. In small bowl blend first 4 ingredients; beat at medium speed till smooth, about 1 minute. Set aside.
In a large bowl, combine all brownie ingredients; beat 50 strokes with a spoon. Spread half of batter in prepared pan. Pour cream cheese mixture over batter, spreading to cover. Place spoonfuls of remaining batter on top of cream cheese. Marble by pulling knife through batter in wide curves, then turn pan and repeat.
Bake at 350* for 30-35 minutes. DO NOT OVERBAKE. Cool; for ease in cutting, refrigerate at least 1 hour. Cover tightly and store in refrigerator.