Preheat Oven:
Preheat oven to 350°F (175°C). Grease or line an 8x8-inch baking pan with parchment paper.
Prepare Brownie Batter:
In a microwave-safe bowl, melt butter. Stir in sugar, eggs, and vanilla. Mix in cocoa powder, flour, salt, and baking powder until smooth.
Prepare Cheesecake Layer:
In a separate bowl, beat cream cheese until smooth. Add sugar, egg, and vanilla, and mix until creamy and well combined.
Assemble:
Pour brownie batter into prepared pan. Drop spoonfuls of cheesecake mixture on top. Use a knife or skewer to gently swirl the cheesecake into the brownie batter, creating a marbled effect.
Bake:
Bake for 30–35 minutes, or until a toothpick inserted near the center comes out mostly clean (a few crumbs are okay).
Cool and Serve:
Allow to cool completely in the pan before slicing into squares.