Preheat your oven to 350°F (175°C). Line a 9×13 inch baking pan with parchment paper, leaving an overhang on the sides for easy removal.
Prepare the brownie batter: In a large bowl, whisk together the melted butter and 2 cups of sugar until combined.
Beat in the 4 eggs one at a time, then stir in 1 teaspoon of vanilla extract.
In a separate bowl, whisk together the flour, cocoa powder, salt, and baking powder. Gradually add the dry ingredients to the wet ingredients, mixing until just combined. Do not overmix.
Stir in the chocolate chips. Pour the brownie batter into the prepared pan and spread evenly.
Prepare the cheesecake layer: In a medium bowl, beat the softened cream cheese and 1/4 cup of sugar with an electric mixer until smooth.
Beat in the remaining egg and 1/2 teaspoon of vanilla extract until the mixture is smooth and creamy.
Drop spoonfuls of the cheesecake mixture evenly over the top of the brownie batter.
Use a knife or a skewer to gently swirl the cheesecake mixture into the brownie batter to create a marbled effect. Do not over-swirl.
Bake for 30 to 35 minutes, or until the edges are set and a toothpick inserted near the center comes out with moist crumbs attached, not wet batter.
Let the brownies cool completely in the pan on a wire rack before lifting them out using the parchment overhang.
Cut into squares. These are great for meal planning ahead of time.
Notes
For the best swirl pattern, use a butter knife and make slow, figure-eight motions through the batter layers.
If you are looking for simple recipes for everyday meals, this two-in-one dessert bars recipe fits well.
Cooling completely before cutting prevents the cheesecake layer from sticking to your knife.