Preheat oven to 430F for 30 minutes to ensure the oven is sufficiently hot when you put the cheesecake in.
Fit an 8 inch round springform pan (3 inches deep), with 2 pieces of parchment paper, leaving a 2 inch overhang folded down over the sides of the pan.
Place the chopped chocolate in a large heatproof bowl.
In a small saucepan over medium-low heat, bring the heavy cream just to a boil, then pour it over the chocolate. Let sit for 3 minutes, then whisk until smooth and the chocolate is completely melted. Set aside and let cool slightly.
In a stand mixer with a paddle attachement, beat the cream cheese, both sugars, vanilla and salt on medium speed. Scrape down the bowl, then add the eggs one at a time, until incorporated. Scrape down the bowl and beat until no lumps remain. Add the melted chocolate and beat on low speed until combined. Sift in the cocoa power and flour and mix until incorporated. Scrape down the bowl until no streaks remain.
Carefully pour the batter into the prepared pan and bake for 35-40 minutes. The top should be dark and the centre should be very jiggly. It will look unset and liquidity. Let cool in the pan on a wire rack for 1 hour, then transfer to the fridge to completely cool.
Remove the cheesecake from the pan and peel the parchment paper away from the exterior. Serve at room temperature.