For the Cookie Crust
- Preheat oven to 325° and grease an 8″ or 9″ springform pan with cooking spray. Make crust: In a large Ziploc bag or a food processor fitted with a metal blade, crush or blend Oreos until fine crumbs form. Transfer to a bowl and pour in melted butter. Add salt and stir until crumbs are completely coated and moist. Press Oreo mixture into pan and 1/3 of the way up the sides, packing tightly.
- In a large bowl using a hand mixer (or in the bowl of a stand mixer), beat cream cheese and sugar together until no lumps remain. Add eggs, one at a time, then stir in vanilla, sour cream, and zest. Add flour and salt and beat until just combined. Pour mixture over the crust.
- Wrap bottom of pan in aluminum foil and place in a large roasting pan. Pour in enough boiling water to come up halfway in the baking pan. Bake until center of cheesecake only slightly jiggles, about 1 hour 30 minutes. Turn off the heat, prop open oven door, and let cheesecake cool in oven, 1 hour. Remove foil and refrigerate cheesecake for at least 5 hours and up to overnight.
- When ready to serve, drizzle with chocolate. Pipe or spoon dollops of whipped topping into small rounds, about 1 inch apart. Set halved Cadbury eggs in the center of each dollop. Serve.