PREPARE FILLING Adjust oven rack to middle position and heat oven to 350°F Line 13- by 9-inch baking pan with foil, allowing excess to hang over pan edges. Grease foil. Process cream cheese, sugar, egg yolk, and vanilla in food processor until smooth.
MIX BATTER Combine flour, baking powder, and salt in bowl. Microwave butter and chocolate in large bowl, stirring occasionally, until smooth, 1 to 2 minutes. Whisk in ½ cup jam; let cool slightly. Add sugar, eggs, and vanilla to chocolate mixture, stirring until combined. Whisk in flour mixture until incorporated.
LAYER FILLING Microwave remaining jam until warm, about 30 seconds; stir until smooth. Scrape half of batter into prepared pan. Dollop filling over batter and spread into even layer. Dollop warm jam over filling and, using toothpick, swirl jam through filling. Spread remaining batter evenly over filling.
BAKE BROWNIES Bake until toothpick inserted in center comes out with few wet crumbs attached, 50 to 60 minutes. Cool in pan on wire rack for at least 2 hours. Using foil overhang, lift brownies from pan and cut into 1½-inch squares. Serve. (Brownies can be refrigerated in airtight container for 2 days.).