• Preheat your oven to 350°F. Line a 9x13-inch baking pan with parchment paper or lightly grease it.

Make the Brownie Batter:

• In a mixing bowl, combine the sugar, cocoa powder, melted butter, and salt. Using an electric mixer or a whisk, combine the ingredients until well incorporated.
  2 ¼ cups granulated sugar, 1 cup unsweetened cocoa powder, 1 teaspoon salt, 1 cup unsalted butter
• Pour in the vanilla and add eggs one at a time, mixing well after each. Stir in flour until just combined then fold in the chocolate chips.
  1 teaspoon vanilla extract, 4 large eggs, 1 ¼ cups all-purpose flour, 1 cup semi-sweet chocolate chips

Make the Cheesecake Layer:

• In a medium bowl, beat the cream cheese and sugar until smooth. Add the eggs and vanilla, and mix until fully combined and creamy.
  16 ounces block-style cream cheese, ⅔ cup granulated sugar, 2 large eggs, 1 teaspoon vanilla extract

Assemble and Bake:

• Pour about ¾ of the brownie batter into the prepared pan and spread evenly (it will be a thin layer).
• Spoon the cheesecake mixture over the top. Drop spoonfuls of the remaining brownie batter on top, then swirl gently with a knife or skewer.
• Bake for 35–40 minutes, or until the center is set and a toothpick comes out with a few crumbs (not wet batter). The cheesecake swirl may puff up slightly and get lightly brown on the edges.
• Cool completely in the pan before serving.