Melt the Butter and Chocolate
Start by adding the butter and chocolate to a heatproof bowl and heat in the microwave in 20-second intervals, stirring each time, until the mixture is completely melted and smooth.
Add the sugar now (brown & granulated). Mix them until the sugar is fully incorporated and the batter has a nice glossy sheen. Make sure to mix it well to avoid any sugar clumps.
take the first egg and add it to the batter, give it a good mix, then go for the next one. This helps ensure a smooth consistency. After that, add the vanilla extract. Be careful not to overmix.
grab a bowl, put into it the cocoa powder, the flour, and the salt, make sure they are well-mixed. This step helps eliminate any lumps.
Next, carefully incorporate the dry ingredients into the wet mixture by folding them together. Stir until just combined.
Making the Cheesecake Layer
Begin by mixing the softened cream cheese and sugar until the mixture is looking good. Use a hand mixer or a whisk to mix them well, making sure there are no lumps left in the cream cheese.
gently fold in the egg and vanilla extract. Mix until just combined.
Assembling the Layers
Pour most of the brownie batter into a 9x9-inch greased or parchment-lined pan, spreading it evenly across the bottom. Be sure to save a small portion of the batter to create the swirl on top later
take your cream cheese mixture and spread it over the first layer (Brownie Batter), covering all the corners.
Now I want you to take the remaining brownie I told you to save, spread it over the cheesecake layer. Take a knife and gently swirl the brownie batter into the cheesecake, creating a subtle marbled design.
Time To Bake
Begin by preheating your oven to 350°F (175°C) to ensure it reaches the perfect temperature for baking. Once ready, pop your pan in the oven and bake for 30 minutes.
I really recommend allowing the brownies to cool in the pan for at least 30 minutes before slicing to ensure they set properly. Remember (at least 30 minutes). This allows the layers to set and makes for cleaner cuts.