To make these bars, use a square or round springform pan, or line an 8x8 baking pan with alumnium foil or parchment paper. Press the cookie dough into the bottom of the pan to form a crust.
In a stand mixer, blend the softened cream cheese, sugar, and salt until the mixture is smooth. With the mixer still running, add the eggs, one at a time. Then add the sour cream and lastly the melted chocolate. Scrape down the sides of the bowl while the mixture is mixing and blend until it is smooth, about 3 minutes.
Pour half of the cheesecake batter into the prepared pan. Sprinkle the quartered Oreo cookies on top. Then add the remaining cheesecake batter.
Bake the cheesecake at 350 degrees for 40-45 minutes, or until the cheesecake has set. Ours took 45 minutes exactly.
While the cheesecake is cooling, prepare the ganache. In a small saucepan, warm the heavy cream until it is hot, but not boiling. Place the chocolate chips in a bowl and pour the warmed heavy cream over the chocolate chips, stirring until the chocolate is completely melted into the cream. Pour this ganache overtop the cheesecake bars and spread it out evenly. Allow the ganache to set. Once the cheesecake is at room temperature, store the cheesecake in the refrigerator. Allow the cheesecake to be in the refrigerator for at least 4 hours before serving.
To prepare the optional buttercream, cream the butter in a stand mixer for about 3 minutes. Add the powdered sugar, cocoa powder, vanill and heavy cream and mix on medium speed for 3 minutes. Once the cheesecake has cooled, pipe the buttercream (with a 1M tip) in a pretty swirl on each bar, or simply use a spoon to put a dollop of buttercream on top.