Waterproof a 9" springform pan by placing 2 18" x 18" pieces of aluminum foil on a flat surface underneath the pan so they form a + then gently fold (to make sure you don't create any holes) up the sides of the foil around the pan. Repeat.* Line bottom of springform with parchment paper and lightly grease the inside of your entire pan with nonstick cooking spray.
Preheat oven to 350°F, with the oven rack in lower third of oven. Fill a roasting pan with 1 1/2 inches water to create a water bath for your cheesecake (to prevent cracking). Place roasting pan in the oven while you prepare your cheesecake.
To make the crust, pour finely ground Oreos in a large bowl and stir in melted butter; mix until well combined. Pour Oreo crumbs into springform and firmly press the crumbs down on the bottom of the pan until you have an even layer.
To make the cheesecake filling, add cream cheese and sugar to the bowl of an electric mixer fitted with the paddle attachment and beat on medium speed 5 minutes until light and fluffy. With mixer still running, add the eggs, then the egg yolks, 1 at a time, mixing 30 seconds after each egg/egg yolk, scraping down the sides of the bowl as necessary. Add the sour cream, lemon juice and vanilla and mix until well incorporated. Pour only 1 1/2 cups of this plain cheesecake on top of the uncooked Oreo crust and evenly spread to the edges. Place in the freezer while you prepare the pumpkin layer (to create more defined layers).
To make the pumpkin cheesecake layer, add pumpkin, cinnamon, cloves and nutmeg to the remaining plain cheesecake batter and mix until well blended. Pour this pumpkin cheesecake onto the plain cheesecake and carefully spread over the plain cheesecake layer.
To bake your cheesecake, place the cheesecake in the water bath and cook for 55-65 minutes OR until the edges are firm and the center of the cheesecake is still jiggly, but not runny.
To gently cool your cheesecake and prevent cracking, turn off your oven and crack open the oven door. Allow cheesecake to cool in oven for 60 minutes, then remove to a wire rack and gently run a hot knife along the edges of the cheesecake. Release springform and continue to cool for 2-3 hours or until cheesecake is completely cooled. Chill in the refrigerator for at least 3 hours.
Prepare topping when ready to serve by beating heavy cream and sugar on high speed until stiff peaks form. Spread whipped cream over pumpkin cheesecake and top with crushed Oreos. Melt chocolate in microwave, mixing at 30 second intervals until melted. Stir in oil and drizzle over cheesecake by placing chocolate in a Ziploc bag, and cutting off the corner.