In a small bowl, whisk together the cream cheese, sour cream, sugar, and flour.

Heat oven to 325°. Line an 8-inch square baking pan with parchment paper and grease with butter.

In a medium bowl, whisk together the flour, baking powder, and salt.

In a double boiler or pan on low heat, warm the chocolate chips and butter while stirring constantly. Continue until fully melted. In another bowl, whisk together the sugar, eggs, and vanilla. Add the melted chocolate butter mixture to the egg mixture and mix thoroughly. Add the flour mixture to the chocolate batter and fold to combine.

Pour ¾ of the brownie batter into the baking pan and evenly spread it using a rubber spatula being sure to get it into the corners of the pan. Spread the cream cheese filling over the brownie batter in the pan. Dollop the remaining brownie batter over the cream cheese filling and spread it as evenly as you can over the cream cheese layer. Use a butter knife to swirl the cream cheese layer and the top batter layer together, creaming a marbled pattern on the top of the brownies.

Place baking pan in oven and bake 20 minutes. Rotate the baking pan 180 degrees and bake another 15 to 20 minutes, until a toothpick inserted in center (be sure to hit the brownie layer, the cream cheese layer will always be gooey) comes out with a few crumbs and no brownie batter attached.

Remove the brownies from the oven and let them cool in the pan on a wire rack for 1 hour. Remove the brownies from the pan uncut and allow to cool for an additional hour on the wire rack before cutting. Serve with a glass of milk.