1. Preheat Oven:

1. Preheat your oven to 350°F (175°C). Line an 8×8-inch baking pan with parchment paper, leaving overhang for easy removal.

2. Make the Brownie Batter:

1. In a medium bowl, whisk together the melted butter, sugar, eggs, and vanilla extract until smooth.
2. Sift in the cocoa powder, flour, salt, and baking powder. Stir until just combined, being careful not to overmix.

3. Make the Cheesecake Mixture:

1. In a separate bowl, beat the cream cheese and sugar until smooth.
2. Add the egg and vanilla extract, mixing until creamy and well combined.

4. Assemble the Brownies:

1. Pour the brownie batter into the prepared pan, reserving about 1/4 cup of the batter for swirling. Spread the batter evenly.
2. Pour the cheesecake mixture over the brownie layer and spread evenly.
3. Drop spoonfuls of the reserved brownie batter onto the cheesecake layer. Use a knife or skewer to swirl the brownie and cheesecake layers together for a marbled effect.

5. Bake:

1. Bake in the preheated oven for 30-35 minutes, or until a toothpick inserted into the center comes out with a few moist crumbs.
2. Cool completely in the pan before slicing. For cleaner cuts, refrigerate for 1 hour before serving.