Preheat the oven to 325 degrees. Line a 9 x13 inch baking pan with parchment paper, allowing it to drape over the sides. Spray with cooking spray.
Place 26 of the Oreos in a ziplock bag and use a rolling pin to smash them into fine crumbs. (You can also use a food processor if you have one). Add the melted butter to the bag, zip it up tight, and shake it until well combined. Press the Oreos down into the bottom of the prepared pan.
In the bowl of a stand mixer, beat together the cream cheese and sugar until well combined, about 3 minutes. Scrape down the sides then add the sour cream and vanilla and beat until smooth. Add the eggs, one at a time, beating well after each addition and scraping down the sides of the bowl as needed. Pour the mixture over top of the Oreo crumb crust. Break up the remaining Oreos (I keep them in larger chunks) and sprinkle on top.
Bake for 42-45 minutes or until the edges are completely set and the center is just barely jiggly. Allow the cheesecake to cool. Refrigerate for at least 2 hours before slicing.
Meanwhile, use a double boiler to melt the chocolate or microwave it in 30 second increments.
Once the bars are cooled, use the parchment paper to pull them from the pan. Use a spoon to drizzle the chocolate evenly over the bars. Allow the chocolate to set for 10-15 minutes then cut into bars and serve.