Preheat the oven to 325 degrees and grease a 9 inch springform pan. You will need a large roasting pan that’s bigger and longer than the springform pan. (I use the aluminum foil disposable ones). If you are not sure about your springform holding up in water, you can wrap the outside of the springform pan in heavy duty aluminum foil from bottom up to the sides.)
Crust:
In a small bowl, combine graham cracker crumbs, cinnamon, and brown sugar, mix very well. Add melted butter, vanilla extract, and pumpkin spice extract, mix until all evenly incorporated.
Spread crumb mixture in the bottom of the springform pan, evenly, pressing it over the bottom and half way up the sides.
Spread chopped Oreo cookies over the crust, evenly.
Cheesecake:
In a bowl of an electric mixer, beat cream cheese on medium-high speed until smooth and fluffy. Scrape sides and bottom on the bowl and beat for another minute.
Add eggs, one at the time, beating after each addition.
Add pumpkin puree, vanilla extract, pumpkin spice extract, and sour cream, beat until incorporated. Scrape sides and bottom on the bowl.
Lower speed and add sugar, cinnamon and corn starch. Make sure that all ingredients are well combined. Scrape sides and bottom on the bowl and beat for a few more seconds, until all smooth.
Pour the cheesecake batter into the pan with crust, over the chopped cookies.
Place roasting pan into the oven and place cheesecake springform pan inside the roasting pan. Carefully add water to the roasting pan, about half way up the side of the springform.
Bake for 70-75 minutes. Turn off the oven and open the oven door half way. Let cheesecake rest for about 5 minutes and take it out of the oven (out of the roasting pan and carefully take off the foil).
Let it rest for 10 minutes on the counter and then gently run a greased butter knife between sides of the cheesecakes and the springform to carefully separate it. (You don't actually have to take the cheesecake out of the pan until ready to serve.)
Cool cheesecake for an hour and then place in the refrigerator. Refrigerate for about 4 hours before adding the frosting.
Frosting:
(Use whisk attachment for frosting.) In a bowl of an electric mixer, add mascarpone cheese, heavy whipping cream, cinnamon, pumpkin spice extract, and vanilla extract. Start on low speed to mix the ingredients and gradually increase the speed over a few seconds to medium-high. Slowly pour in the sugar as the mixture thickens while mixing. Do no walk away, this will be ready fast! Beat on medium-high speed until soft peaks form and gradually lower the speed, over a couple of seconds.
(Don't worry, granulated sugar will melt within 30 minutes or so and it will not be grainy.)
Frost the cold cheesecake all over the top.
Spread finely chopped Oreo cookies over the frosting.
You can serve the cheesecake right away or refrigerate until ready to serve.