In a large mixing bowl, add the butter and the dark chocolate. Melt completely in the microwave or on a bain Marie. Mix with a whisk until silky and smooth.
Add the granulated sugar, espresso powder, vanilla extract, and kosher salt, sift the cocoa powder, and mix with a whisk until well combined.
Add the eggs and egg yolk and mix until well combined and smooth.
Sift the flour and fold the mixture with a rubber spatula until the batter is just combined. Do not overmix. Set aside while you make the cheesecake batter.
Make the cheesecake batter
Into a large mixing bowl, add the cream cheese, sugar, vanilla extract, and sour cream and mix with an electric hand mixer until creamy and smooth.
Add the eggs and mix until smooth.
Sift the cornstarch and mix it until a homogeneous mixture forms. Do not overmix.
Pour ½ of the brownie batter onto a parchment paper lined 9 inch springform pan and smooth it out with an offset spatula.
Pour the cheesecake batter over the layer of brownie batter and smooth it out.
Top the cheesecake batter with dollops of the remaining ½ of the brownie batter and use a butter knife to make swirls. Do not over-swirl the mixture.
Bake the cheesecake in a 170c (340f) preheated oven for 40-50 minutes until the edges of the cheesecake are set, but the middle is a bit jiggly.
Open the oven door halfway, and allow the cheesecake to cool to room temperature for 1-2 hours.
After the cheesecake is cooled, wrap the cheesecake with plastic wrap tightly, and place the cheesecake in the fridge to chill and set completely for at least 5 hours.
Make the chocolate ganache
Melt dark chocolate, and heavy cream in a small to medium mixing bowl in the microwave for about a minute.
Let the chocolate and the cream sit for 10 minutes for the chocolate to melt, then mix until the chocolate ganache is smooth and silky. Reserve 2 tablespoon of the chocolate ganache for the whipped cream.
Pour the chocolate ganache on top of the cheesecake and smooth it out with an offset spatula. Place the cheesecake in the fridge to allow the ganache to set while you make the whipped cream.
Make the whipped cream
Into a large mixing bowl, add heavy cream, powdered sugar, 2 tablespoon of the chocolate ganache that we reserved, and vanilla extract in a large mixing bowl and mix with an electric hand mixer until stiff peaks form.
Pipe the whipped cream with a star tip around the edges of the cheesecake. Serve and enjoy!
Notes
Use room temperature ingredients. It is important that you use room-temperature ingredients like eggs. This step ensures that your mixture mixes into a homogenous mixture and bakes perfectly. you don’t want to place cold batter into the oven.
Don’t overmix the brownie batter. For a fudgy texture, avoid overmixing your brownie batter once you add flour. Mix just until combined to keep from incorporating too much air.
Measure your flour correctly! When measuring your flour, avoid scooping it with a measuring cup. Instead, stir the flour with a spoon to create as many air pockets as possible, and spoon it into your measuring cup. Finally, level it with a back of a knife.
Use high-fat cream cheese or the well-known Philadelphia cream cheese. Using full-fat cream cheese ensures that your cheesecake will be stable and will not crack.
Use a springform tin. We use springform tins for all of our cheesecake recipes. This makes sure that your cake will be easy to release from the pan.
Let your cheesecake chill in the fridge for at least 5 hours. I know it’s very hard to resist eating this delicious cheesecake right away, but you have to let the cheesecake cool and set it in the pan. I like to let the cheesecake sit in the fridge overnight.
For a smooth and creamy cheesecake, make sure that you are using room-temperature ingredients. Before you begin to make this cheesecake, make sure that your cream cheese is completely soft, and that your eggs are at room temperature.
Scrape down the sides of the bowl frequently to ensure that you have a homogeneous mixture that has no cream cheese lumps.
Don't open the oven door before the cheesecake is fully baked or about to be baked! Drastic changes in the temperature of the cheesecake while baking can cause the cake to collapse or crack.