Prepare the Brownie Layer:

1. Preheat your oven to 350°F (175°C). Line an 8×8-inch baking pan with parchment paper, leaving a bit of overhang for easy removal.
2. In a mixing bowl, whisk together the melted butter and granulated sugar until smooth and glossy.
3. Add the eggs and vanilla extract, and whisk until fully incorporated.
4. Sift in the cocoa powder, flour, salt, and baking powder. Fold gently until the batter is smooth and free of lumps. Be careful not to overmix.
5. Pour about 3/4 of the brownie batter into the prepared pan, spreading it evenly. Reserve the remaining batter for later.

Prepare the Cheesecake Layer:

6. In another bowl, beat the softened cream cheese and sugar together until smooth and creamy.
7. Add the egg and vanilla extract, and mix until well combined. Be sure to scrape down the sides of the bowl to ensure a uniform mixture.
8. Spread the cheesecake mixture evenly over the brownie layer in the pan.

Assemble the Layers:

9. Dollop the reserved brownie batter over the cheesecake layer. Use a butter knife or skewer to swirl the two layers together, creating a marbled effect.
10. Drizzle the caramel sauce over the top, reserving a bit for garnish if desired. Swirl the caramel lightly into the top layer for a decorative finish.

Bake and Cool:

11. Bake in the preheated oven for 35-40 minutes, or until the edges are set and a toothpick inserted into the center comes out with a few moist crumbs.
12. Remove the pan from the oven and let the brownies cool completely in the pan. Once cooled, refrigerate for at least 2 hours to set the layers.

Slice and Serve:

13. Use the parchment paper overhang to lift the brownies from the pan. Cut into 16 squares, drizzle with additional caramel sauce, and sprinkle with flaky sea salt if desired.