Preheat the oven to 400 F. Line an 8 x 8 inch baking pan with aluminum foil. Lightly grease the foil with butter or baking spray.
In a medium bowl, stir together the chocolate cookie crumbs, salt, and melted butter. Press the crumbs firmly and evenly into the bottom of the prepared pan. Bake the crust in the preheated oven for 10 minutes and remove to cool. Lower the oven temperature to 325 F.
In a small bowl, combine the sour cream, vanilla extract, and espresso powder.
Carefully melt the 5 oz of chocolate. You can do this in a microwave in 15 second bursts, stirring after each burst, or slowly in a double boiler, stirring constantly. Set aside to cool slightly.
In the bowl of a stand mixer fitted with the paddle attachment, combine the cream cheese, cocoa powder, and salt on medium speed until smooth. Beat in the sugar, scraping down the sides of the bowl as needed until well combined. Reduce the speed to medium low and beat in the melted chocolate. Beat in the sour cream mixture. Finally, beat in the eggs until just combined. Remove the bowl from the stand and give the contents a thorough stir with a rubber spatula to make sure it's well combined.
Pour the filling into the pan and spread it evenly with a rubber spatula. Transfer to the 325 F oven. Bake for 35- 40minutes until the sides are set but the center still jiggles slightly.
Remove the pan from the oven and set aside to cool completely (about 2 hours). Once cooled, cover the pan with plastic wrap and chill in the refrigerator for at least 3 hours.
Place 3 oz of finely chopped chocolate in a medium heat safe bowl. In a small saucepan over medium heat, bring the cream to a simmer. Pour the cream over the chocolate and let stand for a couple of minutes. Stir until well combined. Add 1 tablespoon room temperature butter and stir until smooth and incorporated.
Pour the ganache over the cheesecake bars, and spread evenly. Return to the refrigerator to chill for an extra 15 minutes or so, until ganache is firm.
Slice the bars: Lift the cheesecake slab out of the pan with the foil and place on a countertop. Put a long sharp knife under hot running water and wipe it off. Make one slice, and repeat the heating and wiping of the knife between each cut. You can slice into 9 large square bars, 12 smaller rectangular bars, or 16 smaller squares.
* For the crust, you can either remove the cream filling from some Oreos and crush those, or use chocolate wafers. Wafers are less sweet however, so you may want to add up to 3 tablespoons of sugar if you use those.