Preheat oven to 350°F (175°C). Line an 8×8-inch baking pan with parchment paper or lightly grease it.

Make the brownie batter: In a medium bowl, mix melted butter and sugar. Add eggs and vanilla extract, stirring until smooth. Sift in cocoa powder, flour, salt, and baking powder. Mix until fully combined.

Make the cheesecake layer: In a separate bowl, beat cream cheese, sugar, egg, and vanilla until smooth and creamy.

Assemble: Pour most of the brownie batter into the prepared pan, spreading it evenly. Spoon the cheesecake mixture on top in dollops. Drop remaining brownie batter over the cheesecake layer in small spoonfuls.

Swirl: Use a knife or skewer to gently swirl the two batters together to create a marbled effect.

Bake for 35 minutes or until a toothpick inserted in the center comes out mostly clean with a few moist crumbs.Cool completely in the pan. Refrigerate for at least 1 hour before cutting into squares.