Position the rack in the center of the oven and preheat the oven to 350 degrees. Butter or coat with vegetable spray the bottom of a 9- or 10-inch springform pan. Line a baking tray with parchment paper. Set aside.
Make the crumble: Sift together the flour, cocoa, sugar, and salt, and transfer to the workbowl of a food processor fitted with a steel blade. Process with on/off turns until blended. Arrange the pieces of butter around the flour mixture and process until the mixture resembles coarse meal.
In a small cup or bowl, whisk together the egg yolks and cream with the processor running, pour the mixture through the feed tube, making certain you scrape out all the liquid from the cup. Let the machine run until the dough begins to come together, about 1 minute. (You should have about 4 cups.)
To make the crust, spoon 2 cups of the crumble into the prepared pan and press evenly over the bottom of the pan. (The rounded bottom of a 1-cup measuring cup is perfect for leveling the crust, ensuring smooth edges.)
Spread the remaining crumble on the prepared baking tray. Place the springform pan and baking tray in the oven and bake until the crumble is lightly toasted, 10 to 12 minutes. Transfer to a wire rack to cool. When completely cool, wrap heavy-duty aluminum foil, or two layers of regular foil, around the bottom and halfway up the outside of the springform pan, pleating the foil to tighten. Break up the crumble on the parchment paper, using your hands or a fork, and set aside.
Make the cake: Place the cream cheese, sugar, and salt in the large bowl of an electric mixer fitted with a a paddle or beaters. On medium speed, beat until smooth, stopping often to scrape down the sides of the bowl and under the blade with a rubber spatula. Turn the speed to high and continue to beat until nice and creamy. Stop the mixer and add the sour cream, eggs, and vanilla, beat 3 minutes longer, again stopping the mixer and scraping down the sides of bowl and under the blade as necessary. Stir in the melted chocolate and continue to beat until well combined and smooth. You should have about 6 cups of the mixture.
Pour half the mixture (3 cups) into the springform pan. Sprinkle half the cooked chocolate crumble (1 cup) over, pour in the remaining 3 cups of the cheesecake batter and cover the entire surface with the remaining 1 cup of the chocolate crumble.
Set the springform pan in the center of a slightly larger baking pan with sides. Pour enough hot water into the larger pan to reach halfway up the sides of the springform pan, but not above the foil. Carefully place both pans in the oven and bake for 1 hour. Cover the cake loosely with foil and continue to bake until the center of the cake is slightly firm, 20 minutes longer. (Check the water level after 30 minutes, making certain there is enough water in the pan.)
Carefully remove both pans from the oven and transfer the springform pan to a wire rack to cool. Fold the foil down the sides of the pan, helping the cake to cool. When the cake has cooled remove the foil and allow the cake to cool completely. Cover the pan loosely with a clean piece of foil and refrigerate overnight.
When ready to serve, remove the cheesecake from the refrigerator. Dip a long sharp knife in warm water and run the knife around the inside of the springform pan, loosening the cake from the pan. Remove the outer ring. Continue to dip the knife into warm water as necessary for neatly cut slices.
To serve, arrange a slice of cake on a pretty cake plate and garnish with fresh berries of your choice, raspberries, blueberries, or sliced strawberries.
This recipe yields 10 to 12 servings.