Line a 9x9" square pan with aluminum foil, making sure foil is pressed into the bottom and sides securely. (Lining the pan with foil is optional. It does make it easier to lift the bars out of the pan and slice.) Set prepared pan aside.
For the crust: Crush the 25 OREO cookies into crumbs with a food processor or blender. Add the melted butter, and pulse in the processor a few more times to combine. Pour the crumb mixture into the lined pan, and press firmly to the bottom of the pan. Set aside.
For the cheesecake filling: With a hand or stand mixer, cream together the cream cheese and powdered sugar and mix until creamy and slightly fluffy. Add the vanilla and mix. Gradually add in the thawed whipped topping. Fold in the broken OREO cookie pieces, and mix together. Spread the mixture evenly over the top of the crust, making sure to spread firmly and evenly into corners of the pan. Refrigerate for at least 1-2 hours, or until firmly set.
To make the topping, add the chocolate chips into a bowl. In a small saucepan, bring the cream to a low simmer, and remove from heat. Pour the hot cream over the chocolate chips, and continually stir with a rubber scraper until all the chocolate chips have melted and become smooth. Let the chocolate cool slightly. Pour the slightly cooled chocolate over the top of the cream cheese layer, and spread evenly.
Even place the 16 OREO cookie halves into the chocolate. Refrigerate for at least 30 more minutes or until chocolate is completely set and firm. Cut into 16 squares.