For topping: Preheat oven to 350 degrees. Lightly grease 23 cm square baking pan. The pan must be at least 5 cm deep. Dust pan with flour; tap out excess. Using electric mixer, beat cream cheese with sugar in medium bowl until smooth. Blend in egg, vanilla and salt. Set topping aside while preparing brownie batter. For Brownies: Melt chocolate and butter in heavy saucepan over very low heat, stirring until smooth. Cool slightly. Using electric mixer, beat eggs, sugar, vanilla and salt in a large bowl until thick, about 3 minutes. Stir in melted chocolate, then flour and semisweet chocolate chips. Pour batter into prepared pan; smooth top. Spoon cream cheese topping into pastry bag fitted with 1 cm round tip. Pipe cheese mixture in diagonal lines atop brownie batter, spacing line half to 2 cm apart. Run tip of small knife through cream cheese on opposite diagonal, spacing 1 cm apart and creating V pattern. Bake until toothpick inserted comes out with a few moist crumbs still attached, about 40 minutes. Cool dessert in pan on rack for 3 hours. Cover and refrigerate at least 2 hours. Can be prepared up to 2 days ahead. Run sharp knife around pan to loosen. Cut dessert into dozen brownies. Serve cold.