Preheat the oven to 180C/350F.
Make the brownie base. In a microwave-safe bowl, add coconut oil and semi-sweet chocolate and microwave in 20-second spurts until melted. You can also do this stovetop.
Add sugar and mix until combined. Whisk in the eggs, one at a time, then the cocoa powder and cornstarch and whisk until as smooth as possible.
Transfer the brownie batter to a 9-inch cake pan and bake for 20-25 minutes or until a toothpick comes out mostly clean.
In a mixing bowl, beat the heavy cream until stiff peaks form, then set aside.
In a separate bowl, beat together the cream cheese and sugar until creamy. Add the rest of the ingredients and beat together until no lumps remain.
Gently and slowly beat the whipped heavy cream into the cream cheese mixture until combined.
Transfer the cheesecake mixture onto the cooled brownie base. Cover completely, and refrigerate overnight.
In a small saucepan, melt the chocolate over low heat, until almost melted. Once almost melted, stir in the heavy cream. Stir until smooth and silky.
Pour the ganache over the cheesecake and let it sit at room temperature until it has set.