01 - Preheat oven to 350°F (175°C). Line a 9x9-inch baking pan with parchment paper, allowing an overhang for easy removal.
02 - In a large bowl, whisk together melted butter and granulated sugar until combined. Add eggs and vanilla extract; whisk until smooth.
03 - Sift the flour, cocoa powder, salt, and baking powder into the wet mixture. Fold together just until combined, ensuring not to overmix.
04 - Transfer about three-quarters of the brownie batter evenly into the prepared pan.
05 - In a separate bowl, beat the softened cream cheese until smooth. Add sugar, egg, and vanilla extract. Mix on medium speed until creamy, then tint with green gel food coloring to achieve the desired shade.
06 - Dollop spoonfuls of the green cheesecake mixture over the brownie batter. Spoon remaining brownie batter in small amounts over the top.
07 - Use a knife or skewer to gently swirl the cheesecake and brownie mixtures together, forming a marbled pattern.
08 - Sprinkle with candy eyeballs and Halloween-themed sprinkles, if desired.
09 - Bake for 33 to 36 minutes, or until the center is set and a toothpick inserted comes out with a few fudgy crumbs.
10 - Allow to cool completely in the pan. Lift out using the parchment paper overhang and slice into squares.