In a medium saucepan over medium heat, melt the butter and chocolate together until completely smooth. Then, remove it from the heat, pour the mixture into a large mixing bowl and set it aside to cool slightly for 10 or so minutes.

Preheat the oven to 350°F. Lightly spray a 9x9" square baking pan with non-stick cooking spray, then line with parchment paper, leaving an overhang to easily lift out the finished brownies. Set it aside.

Whisk the granulated sugar into the chocolate and butter mixture. Then whisk in the 3 eggs, one at a time and whisking between each. Then whisk in the vanilla extract.

Next, fold in the flour, cocoa powder and salt. Set this batter aside to prepare the cheesecake mixture.

For the cheesecake mixture, in a medium bowl using a hand mixer, beat the cream cheese until smooth and creamy, about 1 minute. Then beat in the sugar. Once that's combined, beat in the egg and vanilla.

Spread half of the brownie batter into the prepared baking pan. Make sure the whole bottom of the pan is covered with batter. Spread the cheesecake mixture evenly over the batter. Spread the remaining brownie batter over the top of the cheesecake mixture.

Bake for 32-36 minutes, until a toothpick inserted into the center comes out with just a few moist crumbs. If the toothpick is clean, that means the brownies have overcooked.

Place the pan onto a wire rack and allow the brownies to cool completely, then cover the pan and move it to the fridge to chill for about 2 hours. Use a large, sharp knife to slice them into squares once they've chilled. Store them in an airtight container in the fridge for up to 1 week.