• Preheat the oven to 325F degrees.
• Lightly grease a 9x13 inch (23 x 33 cm) baking pan, or line with aluminium foil so that there's an overhang around the edges.

Crust

• Add the cookies (wafers and filling) to a food processor and pulse until fine crumbs. Alternatively, place the cookies in a freezer bag and crush with a rolling pin.
• Mix together the crushed cookies and melted butter.
• Press the mixture into the bottom of the prepared pan, making an even layer.
• Bake in the preheated oven for 8 minutes. Remove from the oven, leaving it turned on.

Filling

• Chop the chocolate into very small pieces. Place the chopped chocolate in a large heat proof bowl, and microwave for 45-second intervals on medium power (not high power, which is often the default). Stir the chocolate between each interval. Repeat the process until smooth. Alternatively, melt in a double boiler over low-medium heat. Place the chopped chocolate in a heatproof bowl. Place the heatproof bowl over the top of a saucepan with a gently simmering water in the saucepan. Ensure that the water isn't touching the bottom of the bowl. Once melted, remove the chocolate from the heat. Set aside.
• In a very large bowl, beat the cream cheese, sugar and cornstarch together until smooth and creamy (about 3-5 minutes). Turn off the mixer and scrape down the sides and bottom of the bowl as necessary.
• Beat in the melted chocolate and sour cream. Again, turn off the mixer and scrape down the bottom and sides of the bowl.
• In a small bowl, whisk together the eggs. Then mix the eggs into the cheesecake mixture about 1/2 at a time until combined.
• Pour the batter over the baked crust and smooth the top.
• Bake in the preheated oven for 30-35 minutes or until the top looks almost set in the middle and the cheesecake has a slight wobble. 
• Turn off the oven and open the oven door. Leave the cheesecake in the oven for about 10 minutes, then remove the pan from the oven.
• Cool the cheesecake fully until it reaches room temperature. Cover the pan and place in the fridge for at least 4 hours or overnight to chill.

Chocolate Ganache

• Finely chop the chocolate and place in a heatproof bowl.
• Heat the cream until almost boiling - either in the microwave using short 30 second intervals or gently in a saucepan over low heat.
• Pour the cream over the chocolate. Let sit for 3-5 minutes, then whisk until smooth. If the chocolate isn't quite melted, microwave for 45 seconds on medium power (do not use high power) and whisk until smooth.
• Remove the cheesecake from the fridge. Blot any moisture off the top of the cheesecake, then pour the ganache over top. Smooth into an even layer. Return the cheesecake to the fridge until ready to serve.
• When ready to serve, take the cheesecake out of the fridge. If you lined the pan, lift the bars out of the pan using the overhang of the aluminium foil - lifting from the long ends. Place on a cutting board. Slice with a sharp knife. Be sure to cut all the way through the crust. For clean cuts - wipe off the knife in between after each slice.