In heatproof bowl set over hot (not boiling) water, melt semi-sweet chocolate with unsweetened chocolate. Remove from heat; stir until smooth. Let cool to lukewarm.
 
In large bowl, beat cream cheese with 1/3 cup of the sugar until smooth. Beat in 1 of the eggs and 1 teaspoon of the vanilla until well combined. Set aside.
 
In separate large bowl, beat butter with remaining sugar until smooth. Beat in remaining eggs, one at a time, beating well after each addition. Beat in remaining vanilla, then chocolate, mixing well. Mix in flour and salt just until combined.
 
Lightly grease a 13x9-inch cake pan.
 
Reserve 1 cup of the chocolate batter. Spread remaining chocolate batter in pan. Spread with cream cheese mixture. Spoon reserved chocolate batter in dollops over top. Spoon jam in smaller dollops among chocolate dollops. With knife, zigzag through layers for marble effect.
 
Bake in 350° oven for 35 minutes or until tester inserted 2 inches from center comes out slightly moist. Let cool on rack. Cut into squares while slightly warm.