1. Preheat the oven to 350°F and line an 8×8-inch baking pan with parchment paper.

2. In a large bowl, whisk the melted butter, 1 cup granulated sugar, and brown sugar until glossy.

3. Add 2 eggs and 2 teaspoons vanilla extract, then whisk until smooth.

4. Stir in the cocoa powder, flour, and salt just until no dry streaks remain. Fold in the chocolate chips.

5. Spread the brownie batter evenly into the prepared pan.

6. In another bowl, beat the softened cream cheese until smooth.

7. Mix in 1/2 cup granulated sugar, 1 egg, sour cream, and 1 teaspoon vanilla extract until creamy and lump-free.

8. Pour the cheesecake mixture over the brownie layer and smooth the top.

9. Bake for 38 to 42 minutes, until the edges are set and the center has a slight jiggle.

10. Cool completely at room temperature, then refrigerate for at least 4 hours.

11. Lift the bars from the pan, slice into squares, and drizzle with chocolate if desired before serving.