Mix the 1 1/2 cups Oreo cookie crumbs with 4 Tbsp melted butter and toss until the crumbs are evenly moistened.
Press the crust into your pan evenly across the bottom. I find it best to use my fingers first, and then switch to an offset spatula or the bottom of a measuring cup to flatten the crumbs firmly in place. Chill in the refrigerator while you continue with the recipe.
Whip the 1 1/2 cups heavy whipping cream with 1 tsp instant espresso powder and 1/4 tsp cream of tartar until stiff peaks form. Refrigerate.
Put the 12 ounces dark chocolate that has been finely chopped into a microwave safe bowl and microwave on high for 30 seconds. Give it a stir and microwave for another 30 seconds. Stir to melt all the chocolate. If necessary microwave an additional 15 seconds to completely melt. Set aside to cool slightly.
Put the 16 ounces brick style cream cheese that has been cut in chunks into your food processor along with the 1/2 cup powdered sugar, 1 Tbsp vanilla extract, and a pinch salt. Pulse/process until the mixture is smooth and silky, scraping down the sides of the bowl to get everything incorporated.
Add the cooled but still fluid melted chocolate to the processor and process again to incorporate everything together completely. Scrape down sides of the bowl.
Now add the whipped cream to the processor and pulse/process to get it combined and there are no large streaks left. Scrape down the sides of the bowl.
Top the chilled crust with the cheesecake batter. Take a minute to spread it out evenly. I use an offset spatula to do this. Get it as smooth as you can.
Cover the top of the pan with plastic and refrigerate for at least 6 hours, or overnight.
Run a thin offset spatula or knife around the edges of the cake before removing the sides of the pan. The cheesecake will keep 3-5 days in the refrigerator and can be frozen for up to 3 months.