Preheat the oven to 350 degrees. Butter the bottom and sides of a 8 inch metal baking pan. Put a long piece of parchment paper in the bottom of the pan, letting the parchment extend up two sides of the pan and overhang slightly on both ends. (This will make it easy to remove the bars from the pan after they have baked.) Butter the parchment.
In the bowl of a stand mixer fitted with the paddle attachment, beat together cream cheese, sugar, egg yolk and vanilla extract until combined, about 1 minute; Set aside.
In a small bowl whisk together the flour, baking powder, and salt; set aside.
In a small, heatproof bowl, melt butter and chocolate together. Stir until combined and very smooth. Whisk in 1/4 cup jam and set aside to cool for 5 minutes. Add sugar, eggs, and vanilla to the chocolate mixture, and stir until combined. Whisk in flour mixture until just incorporated.
Microwave the remaining 1/4 cup jam until warm, about 30 seconds, and stir until smooth.
Spread half of brownie batter into the prepared baking dish. Dollop the cream cheese by the spoonful over the batter, and spread into an even layer. Drop spoonfuls of warm jam over the cream cheese, and use the tip of a knife to swirl jam through the filling. Spread the remaining batter evenly over the filling.
Bake until a toothpick inserted into the center comes out with just a few dry crumbs attached, 50 to 60 minutes. Cool in the pan on a wire rack for at least 2 hours before lifting out the parchment paper to remove the brownies.